It's what I've used everywhere I've worked for 20 some years, going back to Win3.1. At home, I've got several major apps I use that are not available for other platforms. Then there's just plain inertia.
Macs are looking more enticing. Wish there was a standalone box between the Mini and the Pro.
I like it because of its flaws, they make it fun to explore and manipulate. Plus the fact is supports the most software out of all of the OSs, so thats why I use it, oh and the fact that I hate the layout of Macs and I've seen Linux.
I use Windows over another operating system because I have been working in Windows since I was 8 years old and now the language of Windows seems like second nature to me.
There are lots of programs available for Windows for what I am looking to do (animation, game design, website design, etc)
The only OS I would switch to would be Macintosh since there are some better video programs for it.