Yes. I use mostly Windows, but also own a couple macs, an XT running DOS and a laptop with a WinXP/Linux (I forgot the distro) dualboot (which is my main machine). I guess dualboot counts, so...
(And if we are also counting VMs, I got 3 more Linux systems XD)

EDIT: 8+ computers, 3 people (including me) and 1 dog...yeahhhhh...

EDIT 2: Forgot about the new laptop. The Win7/Debian dualboot I tried to hijack Android with.