Vista

Vista on my desktop and XP on my work laptop.

We have an iMac too...not that I get to use it often :( 

OSX on my MacBook.

Windows XP corporate edition, I'll never use Vista unless XP support drops off and I have to!
Even MS knows Vista sucks, and it follows the system; every other Windows is horrible in my eyes and every other is brilliant (to the extent Windows is brilliant that is...).

XP

I use XP for my office and home PCs. I also have played with Fedora Core 6, but removed it in favor of Ubuntu 7.10 after playing with it. I also have access to a Vista machine but don't like using it unless I must. I tend to use the Vista machine as a jukebox since it is in my office as well.

Again XP with a side playbox Ubuntu.

iBook - Mac OS X (10.4.11)

iPhone - iPhone OS

PS3 - Sony OS

Completely Windows free, it's great :D

Gentoo on two machines
Gentoo on wife's laptop
Xandros on the EEE PC
OLPC on the XO

also have Gentoo loaded on the PS3 as the "Other" OS.

Also got a mac mini running OSX leopord.

OSX

Mac