last time I was in paris was 10 years ago as a starving student, so just about everything I know about paris is probably pretty useless.
only bit of advice I'd have is to at least greet people in french, and then apologize for not speaking more french...that seemed to work pretty good for me. and if anyone, upon recognizing you're american, attempts to tell you how crappy the US is and how much they hate george bush, just don't bother engaging it/try not to engage it if possible. whether you like GW or not is really irrelevant. you can tell them you hate GW and our current policies and they'll still complain to you, or you can tell them they're full of shit in which case you'll end up in an argument.