What OS(s) do you use?

[AutoHappiness]

I use Windows 7. I once had a dual-boot on my laptop between W7 and Ubuntu.

[Bmotley]

Dual boot Win 7 and Ubuntu on my laptop, desktop has XP.

[morgoth]

Desktop dualboot Win7 pro/Kubuntu
laptop dualboot Kubuntu / win 7 pro (haven't booted win for months )

[antil33t]

OSX, Laptop mostly.

Win7 on desktop, laptop is far more convenient for 99.9% of use.

[1macfan]

Laptop (MacBook Pro) running Mac OS X ("Lion").
As well as Windows 7 ( running under Desktop Parallels).
Works pretty good (especially for Automation).

[Zephyroth]

Windows 7 Home Premium 64bit

Greetz,
Zeph