I studied french in high school, and a bit in college, but unfortunately when I actually took a trip to France, there was a grand total of ONE, that's right ONE person I met there who didn't speak English. It is useful to know French in Quebec though...it seems that just about everyone there also speaks English, but just making the attempt to speak French seems to make the people you meet a lot nicer. Instead of being some ignorant American, you become someone who has made an attempt to appreciate their rich French culture...or something like that.
I also took a little bit of Mandarin in college, which is actually quite useful because there are about a billion people who speak it, and most of them don't speak English fluently.