I personally prefer Windows. I would switch over to Linux but I can do much better multitasking with windows. Macs are just impossible for me to multitask with and Linux kinda has less space per resolution so I feel kinda bloated.
I don't game on PC but Windows has some of the best programs that I like and use everyday. They are possible to run with Wine and stuff but they don't run well on linux. The programs that are keeping me on windows are megui, media player classic (don't like VLC), Notepad++ and many others.
Also because it's actually possible to have portable programs for windows. So if I reformat or sth. I don't have to reinstall any of my programs. I can also go back and forth between XP and VISTA while keeping all the same programs and firefox bookmarks and stuff. it's completely awesome.
And another thing is that there are MANY programs for windows for a specific task, while on linux or mac, I'm pretty much limited to 2-3 programs. So, if I don't like 'em, I am screwed. While on WIndows, I have a choice of many programs. Take Video players for example, I presonally don't like any other program besides Media Player Classic. I have given EVERYTHING a try but they all suck. On linux, I'm limited to VLC or MPlayer. while on mac, I'm just limited to VLC.
And also because Microsoft doesn't release a useless update every year that I have to pay for. All the service packs and stuff are free, which is awesome. And I'm not forced to update to Vista unless I absolutely want to.
I think Ima wait till Windows 7 to update.
And of course, I am free to update my hardware in any way I can.
I use Windows for everyday stuff and linux just for live CD whenever something goes wrong, which has never happened to me but I'm prepared lol.