As the title says, why do you still use Windows? What ties you to that operating system?
For me there are probably a couple of answers:
There are some games that just won't run on Linux or could potentially be a pain to get running (like under Wine for example). Although I've taken to playing a lot of cross-platform open source games like some of those found here, I do still like some commercial games, as does my family. Trying to get those games running on Linux just wouldn't fly, especially for family members.
As for other alternatives, I just don't like the Mac. I'm used to doing things in Windows and I find that I'm constantly tripping over myself on Mac OS X just to do the simplest things. I can't for the life of me understand why when you close a window, the app doesn't close. I guess it's just a different way of thinking but I find it irritating. In addition, that is to say nothing of my loathing of Apple; and people talk about Microsoft abusing their position of power?
Anyway... this is starting to sound like a rant and in danger of becoming a TLDR thread. There are reasons why I still use Windows and don't plan on stopping any time soon. What are yours?