We use it all the time, with great success. We have one Dropbox (free account) for kids to keep their programming, drawing and other stuff in (one folder per kid). They lose their stuff
all the time, in the most creative ways possible. Dropbox's 30-day version history can be a real lifesaver in those cases.
Although sometimes stuff is just gone and they're out of luck. I'm still not entirely sure what happens then, possibly a weird combination of everyone saving their project near closing time, the Internet connection maybe choking up a bit, and people shutting down their computer before everything is properly synced.