The Main Difference between Europeans and Americans...

Feeling of Time & Distances
Perception is shaped by our environment. A 100-year old house or church is considered new by Europeans, but old by Americans. I have even heard Americans think that 200 years was "ancient". For a European "ancient" refers to something that is typically 2,000 to 5,000 years old (related to the Antiquity, not antiques !).
Things are reversed when it comes to distances. Europeans would tend to think that driving 100 km is quite a long way, while for Americans that would be rather near. This is due to the much higher density of population in Europe, and the smaller size of Europe (believe it or not the EU is over twice smaller than the USA). Yet, Europeans usually travel more than Americans, inside or outside their own continent. This might be because Europeans are used to go "abroad" since their childhood, European countries being so small, and do not feel the whole experience to be so exceptional. Supposedly Seattle residents feel the same about going to Canada, a stone's throw away.

Cars
Almost all Europeans have cars with manual gears, while Americans have a marked preference for automatic ones.
European cars are also very different in style than their American counterparts. American cars tend to be more massive and squarer, because size matters in the States. Americans have a fondness for (very) long limousines as well as pick-up trucks (in the country). Both are virtually unseen in Europe. Europeans like rounder designs of cars. Smaller cars are much more common in Europe, probably because Europe has a more urbanised population and small cars are easier to park in cities (especially on pavements of historical cities where big parking lots are rarer than in the USA). Much more Americans drive luxury cars, such as BMW, Mercedes, Ferrari. More than half of the American cars are jeep.
Americans almost never walks, except in the big cities (such as NYC, Chicago, San Francisco etc)

Housing/Living
Americans prefer to live in big houses, whereas in Europe most people live in much smaller apartments and housing. More than 80% of Americans live in a house and townhouse, whereas in Europe over 80% live in apartments. Most houses in the USA are newer and luxury, whereas in Europe they are older and basic.
Almost every adult in the USA have their own car, and every house could have 2 to 4 cars, whereas in Europe every family has only one, or maximum two cars.
Europeans use public transportation much much more than Europeans (only New York City and other few cities, such as Chicago and San Francisco residents almost only use public transportation). American thinks: The bigger, the better.

Washing machines
European washing machines normally have only a cold water inlet (the water brought to adequate temperature inside the machine) as opposed to a hot and cold water inlet in the USA. European washing machines are almost always loaded from the front, as opposed to both top and side in USA. Interestingly, Japan decided to follow the American system. Washing machines are also bigger and faster, with more programs and options than European ones.

Measurement System
All Europeans use the metric system (metres, grammes, litres, Celsius, etc.). Although Americans do learn it at school, the vast majority of them still use the old English Imperial system (yards, miles, pounds, Fahrenheit, etc.) for everyday life. However, everything is labelled both in metric and imperial units in all packages, food and other items in the USA.

Date and Time system
Europeans write the date in the format "Day Month Year", whereas Americans use "Month Day, Year". Americans usually consider that the week starts on Sunday and ends on Saturday, while in Europe it always starts on Monday and finishes on Sunday.
Most non-English-speaking Europeans use the 24h system, as opposed to the 12h system used in English-speaking countries.

Public holidays
Labour Day (1st May) is a national holiday in (most) European countries, but not in the USA. USA's Labour Day is first Monday in September. EU countries also celebrate Europe Day (5th or 9th May), although it is not an official holiday (yet).
Social customs
Europeans think of "traditions" like baby showers and bachelor(ette)'s night with strip-teasers as typically American (which they are). This is something most Europeans only see in US series and movies. The same is true of Thanksgiving and, until the late 1990's, of Halloween (but this last one exported itself well to Europe and East Asia).

Schooling
Schools and universities are free in most European countries. Europeans see university as granted, while American families often have to save for years for their children to attend one. What is more, universities in most countries around the world have entry exams, while only a few European countries do (like the UK).
North Americans have prom night at the end of the last academic year of high school (and sometimes also middle school), while Europeans have no such tradition.
Going to University is very important for Americans.
American kids usually discuss where to go to college, whereas Europeans never talk about college.

Languages
Foreign-language learning in Europe is now compulsory in every country since primary (elementary) school. Most Europeans learn 2 to 4 foreign languages, for obvious reasons. Americans usually only speak English (+ their mother tongue for immigrants) because they do not need more in their huge country, and English is world language. However, most kids learn Spanish or French as second language.
Politics
Europeans tend to be more liberal regarding soft drugs, prostitution, alcohol, abortion, or cloning (but interestingly not so for GM food). Americans on the contrary grant greater freedoms when it comes to gun possession, as well as driving a car from a relatively young age (the norm is 18 years old in Europe).

Government system
Americans have a "Congress", while Europeans all have "Parliaments".
American politcs is chiefly curtailed to two parties, which would be center-right and right, but lack influential left-wing or green parties. It is rare for a European country to have less than 3 main parties. It is often 4 or 5, which makes politics less bipolar (but often also more complicated to reach agreements).

The American police (FBI) is much more "aggressive" than the police in Europe (car chases, break into houses with guns shouting "police, don't move, hands on your head !" or such scenes almost non-existent in Europe). Suspects in the US are detained more easily and interrogated more harshly. Americans also go to court much more promptly than in Europe.

The legality of guns in the States also makes daily life and one's sense of safety completely different from Europe.

Patriotism
Americans put much more emphasis on patriotism than Europeans. Being a patriot is a way of life in the USA. The term is rarely used in Europe.
Few Europeans would mind rational critics of their country's government, while a good deal of Americans find them offensive or disrespectful (especially from non-Americans). Some Americans go as far as regarding criticism of their government as a personal attack. Europeans are only too happy to hear other people criticising their own politicians or their country's problems.

Religion
Americans are much more religious than Europeans. Church going is very popular in the US, where it is seen as an indispensable way of socialising. In Europe the practise has almost entirely disappeared and is mostly limited to the elderly, or special events like weddings or Christmas.
God is often mentioned by American politicians, but almost never in Europe. Mixing religion and politics is taboo in many European countries (notably France), due to the stricter separation of state and religion. There are exceptions, such as Poland or Spain, but even these countries do not appear very religious compared to the USA. Lots of Americans have religious cross inside their car on the front mirror.

More extremely, a majority of Americans would find offensive for someone to openly claim not to believe in god, whereas the opposite is often true in Europe.

Circumcision
Circumcision is almost unheard of in Europe, as in most of the non-Muslim and non-Jewish world. The practise became very popular in the USA after WWII, and over 90% of baby boys born during the Cold War era (until the 1980's) were automatically circumcised, with or without their parents' consent. It is becoming less common nowadays. Nevertheless, a 2002 survey revealed that 79% of American men were circumcised. The prevalence was lower among Hispanic men, and lowest of all in men born outside the US.

Political correctness
Due to their great ethnic and religious diversity, Americans have developed a more acute sense of political correctness, in an attempt to attenuate frictions between the various groups. Europeans still associate very much with their place of birth with their ethnicity, language and culture. In fact, until recently, adjectives for language, ethnic group and nationality would often match (with notable exceptions, like Belgium and Switzerland). In the US (almost) everybody has the same nationality and language, and it is ethnicities and religions that differentiate people first, hence the greater importance for respect toward other ethnicities and religions in the USA.
In Europe the emphasis of respect is put on cultures and languages. Making aggressive jokes about a particular linguistic or cultural group (e.g. calling the French "cheese-eating monkies) because of the importance of cheese in French culture), for instance, is the equivalent of attacking a particular ethnic or religious group in the US. It's a big no-no. However, making fun of religions is usually quite acceptable in Europe.

Food
Europeans all have a lot of traditional dishes from their region or city. Specialities tend to be very local, so that some pastries can be seen in one town, but not 100 km away.
Europeans eat more varied and balanced meals (especially in southern cultures) and less fast food than Americans (except maybe the Brits). Europeans eat more cheese (not just the French !), more yoghurts, and on average drink more wine and stronger beers than Americans.

Americans consume sweeter food and much more soft drinks than Europeans. US alcohol laws are much tougher than anywhere in Europe (legal age 21 in USA, and 18 in Europe). Americans also tends to eat outside, on restaurant and fast food much more than Europeans. Portions are larger in the USA.

Sports
It is interesting how the popularity of sports can be so different between Europe and North America. The most popular sports in ALL Europe is football (soccer), probably followed by tennis, cycling, and Formula 1 (as well as other motor races). In the US, soccer and F1 are far away in the popularity ranking. It is baseball, basketball, ice hockey and American football that attract the crowds and make money. And as much as European sports lack popularity in the US, the reverse is true (except for basketball).

Dating & Marriage
While marriage is increasingly seen as a completely optional "folkloric tradition" in Europe, it is still quite important in the USA (probably because religion is also more important there). Statistically Americans marry much more than Europeans, Gay marriage, now legal in several EU countries and hardly an issue for debate in Europe (because of the little importance of marriage in Europe nowadays), is still vehemently opposed by a big part of the US population.
Wedding ceremonies are also much more important and formal in the USA. In most of Europe it is limited to an informal family gathering (usually at the bride or groom's parental home). Marriage traditions do vary considerably between European countries, and even more between families. But in average it is certainly less important than in the States (or in Asian countries for that matter).

Furthermore, there are some strong nationwide American traditions regarding wedding ceremonies, like bringing "something old, something new, something borrowed, and something blue". There is obviously no equivalent thing at a European level, and most often not even at a national or regional level.

In fact, even the way of dating tends to follow so well-defined rules in the USA. For instance, there are widely followed conventions about sleeping on the 3rd date. Men know they shouldn't expect to see a woman again if she insists to split the bill ("check" in AmE) at the end of their first date. The way of proposing, or buying an expensive ring are more important for Americans too. In Europe, the way of doing things is more informal and spontaneous, and can varies a lot from one region to another, and even on a person to person basis. Sometimes, that makes Europeans envious of how easy and clear things look in the USA in comparison. The drawback is that it seems too stereotypical, especially if you don't like the conventions.

Nobility
Europe still has a class of noble people (restored in Eastern Europe after the fall of communism), and many countries will mention the title (e.g. Baron) in official documents. About 1% of family names still have a "noble particle" (uncapitalised "de", "di", "von", "van", etc.) and it does have a meaning for some people. Europe also has hundreds of thousands of castles reminding people on a nearly daily basis of the time where nobility once ruled over everything.
Military politics
It is prohibited in most of Europe for the military people, or anyone with a professional military history to become a politician. This means that they become politically ineligible. In the USA, the reverse is almost true. It is almost required to have a military history to become president, and quite a few Congress people have also served in the army. Maybe this is because the president's image is still strongly associated with that of the "commander in chief", and because defence (or offence) is so important in US politics.
Let's also note the common use of gangsters and criminals in the US military for their "killing talents", and the way they can pass from notorious criminals to national heroes - something mostly unheard of in Europe. The US government has even used this tactics in post-war Japan to fight communism by forgiving and rehabilitating convicted war criminals and yakuza leaders (some even became Prime Ministers with the support of the US, like Kishi Nobusuke).