I’m using xp on a computer that was built from scratch with all new parts 3 years ago. I figure I’ll upgrade my 3 year old homebuilt computer to windows 9 when it comes out, or at least attempt it. If it won’t go, then I’ll switch to linux. Until then, I’m sticking with xp...and skipping vista, 7, and 8.
My wife is also on a home built computer using Windows XP. She’s got a laptop with 7 on it, but is perfectly content to keep using the old OS on her desktop. She’s got so much work tied in with the old OS, that she’s more comfortable leaving things the way they are, until such time that she’s forced to upgrade.
Myself, I’m happy with Windows 7. I’ll probably stick with it until someone pries it out of my fingers :-)