Originally posted by Pocket:It depends on the game. Valve games like Half-Life 2 store your progress and stuff on Steam Cloud, so they'll be re-synced when you start from a fresh install, unless you've disabled it. Most other games will store their data somewhere in your user folder, so if you uninstall and reinstall immediately on the same machine (though why you would do that I can't imagine), they'll still be there but if you're migrating to another computer, or wiping your computer and reinstalling the OS, you'll have to hunt them down and transfer them manually.
Originally posted by Pocket:I believe it does as of the big update last year. I can't vouch for settings and key bindings and such, since I've never changed mine, but save files for single player games do sync.