I use Windows XP most of the time, although I do have Windows Vista Ultimate x86 Build 6000 (final) on another drive. I've used Ubuntu and Kubuntu Linux, but I suppose I'm just to used to how windows works, having used windows since I was 3, I don't think anyone can blame me for that lol! I've also used Mac OS X 10.4 - and its pretty good, but the OS seems a little, well slow, and transitions seem to get in my way a lot, and Photoshop, oh my god, it doesn't have a background! What is with that! I love having a nice gray background on Photoshop on the PC, since I usually have it spanning across my 2 screens, and lay stuff out on it like I would a separate table, because I wouldn't lay out photo prints on the kitchen table when it has food on it, so why wold i lay my stuff out in photoshop with the desktop right behind it!
I still stick with XP - but XP is broke, Microsoft admitted it, some of the flaws are "un-fixable" and are down to the core architecture of the OS and the file system, which was supposed to be changed for Vista, but the new WinFS file system was dropped for Vista, more than likely to cause more buss for "Windows 7" or "Vienna" (or even "Blackcomb" as it was first known) but thats 2009-2011 material lol!
I'll probably only use Vista for gaming (DX10) besides the XP interface is really customiseable, but the hardware acceleration for the GUI in Vista means even more outrageous UI concepts can be done without slowing the machine (making the gpu do all the UI work rather than putting the load on a CPU that is trying to deal with other things.
Anyway, XP for now, Vista for games, OS X 10.5's Dock looks amazing, oh and you can run OS X 86 on your ordinary PC providing it supports SSE2/SSE3
Canon EOS 5DmkII + BG-E6 + Canon EOS 40D + BG-E2N + Canon EOS 33
Canon 17-40 F/4L
USM + Canon 24-70 F/2.8L
USM + Canon 28mm F/1.8 USM + Canon 70-200 F/2.8L
USM IS + Canon 85mm F/1.8 USM
Canon Speedlite 580EX II + Canon Speedlite 540EZ + 2 x Nikon SB-80DX
Cactus V2s Wireless Trigger - 5 x
Cactus V2s Wireless Reciever