I'm also Windows Free™, but my family isn't and I don't use OS X exclusively.
I have my MBP which runs Leopard only. I have a PC that I use as a server that runs CentOS Linux, and I have a PC laptop that runs Ubuntu. I have another (headless) laptop that also runs CentOS.
My dad has an XP box which I want to get rid of soon, and my sister has a Mac mini with Tiger only.
And the only Microsoft product that I own or use at home other than Windows is Office 2000 for Windows.
I use OpenOffice and iWork everywhere else.
But I would love to use OS X exclusively... I can't stand Windows and Linux also has its moments (lack of drivers).