DuoLingo iPhone App
Language learning is definitely something that lends itself to doing here and there when you have some downtime, like standing in line, sitting on the train, waiting for the movie to start.
So if you really want to learn a new language or improve your mastery of another language, check out DuoLingo on the iPhone. It's an entirely free app and they are supporting French, Spanish, and German to start. More languages will be coming soon.