Which operating system do you use, and why?

[CapAmerica]

Primary computer Mac OSX 10.4.10,
Because I've used so many different OSes and I Like the Mac OS by far the most.
It's very stable, has no viruses or spyware, its easily to work with, it works fast and efficient and it looks great. I can't ask for anything more in a OS. Apple makes Amazing products!

Gaming PC I dual boot Windows XP Media Center and Vista
Why... Well I have very few choices when it comes to computer gaming, If I want to play PC games I need Windows sadly and I installed Vista cause I got it for free and DirectX 10 only works in it. So what choice do I have? eventually I'll probily stop playing PC games and just wait for games to be ported to my Mac or stay with consoles.
Hooray that UT3 and StarCraft 2 are coming to the Mac!

All most forgot, My PC laptop runs Ubuntu. Best version of Linux todate. Easy to use (for Linux). I just needed something that ran on a 1Ghz Dell laptop that wasn't Windows. All I use it for is writing, listing to music, checking email and surfing the web