It's not about the money (for me). I just don't like microsoft or apple.

Since I started running linux (almost 4 years ago), I've never had to:

Scan my computer for malware
Scan my computer viruses
Clean my registry for errors
Defrag my hard drive
Do a complete reinstall due to sluggish behavior
Reboot because of a locked up application
Pay $100+ for it
Pay more $$$ for virus detection/removal software

I'm not a huge gamer, so the fact that many games may not work isn't a problem. It's been getting progressively better over the years and many games will run on WINE.

I find applications are better written for a Linux desktop since it's not corporate fluff doing the thinking. It's made by real users.