Hmmm ... I got involved in customizing Windows so that I could create something like the desktops available on UNIX systems and the alternate desktop for Windows 3.x produced by Central Point Software back in the day. Having spent many years developing on Windows and many flavors of UNIX, I can say this about the Linux/Windows debate.
Windows is friendly, has an enormous variety of easily installed major applications available, is a resource hog, and is still (even with XP) unstable. I've had numerous occassions where Ctrl-Alt-Del didn't work and I've had to reboot.
UNIX (including Linux) requires more user sophistication, is limited in the available major applications, but has lots of very useful utilities, is extremely stable, and offers much more user control. And it's FAST.
Bottom line, I found myself FTPing frequently between the systems, doing routine work like editing and email on Windows and running critical programs on UNIX. It all depends on what you want to do and what you want your computer to do.
Finally, unlike Billyware, with UNIX you're not limited to the GUI that comes packaged with the OS, so the Linux people have less need to spend their time customizing the interface and can spend more time doing real work -- like creating a new game for Windows users.