Vista here. It's difficult to use at first because it's new. However, once you get it figured out, you're set.
XP for Work, OS X Tiger for home. Being a bit slow, I was using OS X Panther for home. I then bought a new Ipod Nano......doh! Had to buy Tiger. Thanks Apple.
Currently using Windows Vista, but I would much rather be using XP. Vista bogs down my memory very badly and I even have 3 Gigs of Ram too.
I use Mac OS X Leopard. Just switched from windows a few weeks ago and i will never go back to a PC/windows!