I use XP.
I had windoezzz vista, but then switched to linux, and, after being pissed off at wine, decided to switch back to windows. Thing was I couldn't find my backup CD, so I had to use this XP installation disk.
The whole thing taught me that I don't really care about the OS, as long as I can play video games. (and code in DBPro!)
errm, actually, I had like no crashes or freeze ups with linux. I would have preferred to stick with linux, but I had already invested a ton of time getting everything working (Arch Linux) and the realization that I would have to tinker for hours every time I wanted to get a new DirectX application running just set me off.
errm, the downside is that XP is like the most virus prone OS out there, since it's been out the longest and people like to target windoezzz.