One thing that might come as a surprise (or might not) is using the formal way of speaking. Polish, as many languages, has a formal and an informal way of speaking. English just has the all-encompassing "You." For instance, if I were to ask a question to someone my age, I might say, "Jak sie czujesz?" (How do you feel?); however, if addressing an elder or someone of rank I would say, "Jak sie Pan czuje?" (How do you feel? (formal) Lit: How does Mr. feel?) This seems fairly simple. But, what if you're speaking to the mother, whom you know and everyone else just addresses as "Ty" (informal "you")? Ought I to use "ty" or "Pani?" Also, since I don't have a firm grasp on the language, using the "Pan/Pani" form is slightly more difficult when asking complicated questions. It's kind of the same as in German, but they just have the Sie form which makes everything easier (even easier than the informal way.)
A friend of A's lives in The States and has remarked how he never opens doors for women because they might get offended. I've grown up with this fact and it has come back to be a major source of friction. The women here see it as expected and that if a man does not do it, he's horribly rude. On the other end, I was taught to wait until everyone at the table was seated to begin eating (especially at large dinners such as Christmas and Thanksgiving.) At Christmas Dinner, I waited a full ten minutes for A, who was out walking the dog. In the meantime, her entire family has cleared their plates and had started on seconds, all the while urging me to eat.
Another this is that half the table left to watch Harry Potter on TV.
While it's taboo to go through the door before the woman, it's perfectly acceptable to claim that her place is in the home taking care of the children. (See a previous post.)
Some things span cultures: picking your nose and/or urinating in public, calling a woman fat, refusing to shake hands, etc.