For basic desktop use, I find 800 dpi to be good. In a game like tremulous, I found a sweet spot with 2000 dpi and bind scripts changing the sensitivity depending on whether I was humans or aliens. With Savage2, 2000 dpi seemed to be messy. Razertool gave me a simple way of changing the mouse settings on the fly by having my own startup scripts for the games I played. I really miss this functionality in my current mouse.
Yes, I'm one of the few that doesn't dual boot to play games, I like Linux.