Table etiquette on both sides of the Atlantic

As most travellers know, the idea of good table manners is different on both sides of the Atlantic:

In Europe, while eating a main course (still wondering why it is called entrée in the US), we hold the fork with the left and the knife with the right hand, cut the meat and eat every freshly cut morsel immediately, whereas Americans first cut all the meat and possibly the veggies into handy bits, put down the knife and use the right hand to eat with the fork while keeping their left hand under the table.

It is sometimes frowned upon if you do not respect these rules, as Americans think that Europeans have a barbarian atbreastude towards their food, whereas Europeans find it pretty childish to see an adult person cutting his food into dice before eating it (and what the heck is the guy doing with his left hand under the table ??)