I've been using Dropbox since before Dropbox was invented. (Apparently people feel like announcing that they've been using Dropbox for longer than everyone else makes them cool, so I thought I'd outdo them). In all honesty though, Dropbox is the most impressive sync I've ever come across, and has been indispensable for me. I use it only for critical files that I need on two computers at once, so I haven't hit the 2GB cap, though I'm thinking of doing the paid program just to contribute to the project's longevity.