Myself, I have 4 desktops, The Socket A Win 98 machine isn't online and doesn't really count but other 3 are: main gaming/work machine: Win 7 - best thing ever to escape from Redmond

Audio/Video editing machine and also XP exlusive games: Win XP. Goes flakey now and then but still a pretty good OS. Media machine: Vista. I bought it so I'm going to use it. Fortunately media machine doesn't really need speed which is just as well as Vista has the speed of a snail skateboarding through molasses.
I used the trial version of Win 8 and didn't like it from the off but thought I'd make an effort. After spending some considerable time in an effort to like it, I ended up hating it even more.
Win 8 - the 2012 version of Win ME
PS: I also regularly mess with Linux Distros, currently using Mint 12 KDE on a regular basis.