You know you have lots of international friends when you're saying your "hello"s or "goodbye"s and you've no idea what's appropriate for the given situation.
I remember learning the bisous in French class back in 8th grade. That's a sort of kiss wherin you touch cheeks with the person you're greeting or saying your au revoir to. My 13 year old self had to walk around the room, exchange "Bonjour!" or "À tout à l'heure!" with everyone and actually touch the cheek of another person - even boys in a few of the cases! My cheeks were burning by the end of it. Our French teacher told us that in France, people only hug if they're sleeping together. All that full-frontal action seemed, to her and her wannabe culture, perverse.
I'll tell you something perverse. When you get mixed up between the different cultures' bisous (some start on the right side, some on the left, some go once, others twice, some obnoxious Frenchmen just don't know when to stop...) and you end up touching lips. I did that once. I was so embarassed, I had trouble looking at him for the rest of the soirée.
Germans, although you may not expect it, are born huggers. They want to hug to say "hello" and they'd rather hug than wave "goodbye;" even if you aren't sleeping together. Sometimes I feel them moving into it and I know to keep a respectful, one meter distance, with a single hand raised to move from side to side: my friendly wave.
Americans are also known huggers. I'm not averse to hugging per say, I just need to like you a lot before we move that far. I recall being perturbed more than once in the States by someone hugging me hello or goodbye and I felt like, "What is this? I don't know you."
Americans also give good handshakes. I'm a huge fan of a good, firm handshake. Along the same line: If I have to move into The Hug, it's not so bad so long as it's somewhat meaningful and firm in its own right. There's some dude I know who gives the emptiest hugs. Now that's just wrong.
I honestly wish that everyone did the bisous. To me, it feels meaningful, but not too close. I feel like you can express emotion through it quite easily, and just as lightly leave it to formalities. I don't even mind the inconsistencies of this gesture in different regions and cultures; it adds a little bit of excitement to the experience. Germans will sometimes do the bisous when thanking you formally for a gift or something. That's if they know better than to hug you.
I think it'd also be cool to live in a culture where bowing was commonly used.