I've been having a crap-ton of fun with VMWare Fusion. Running Snow Leopard, Ubuntu, Win XP, and Win 7 on my Mac Pro simultaneously using Spaces... so each space has a different OS.
I'm really over the Mac vs. PC debate and just think people should use whatever they know and are going to be productive using... That said, and hardware considerations aside, any claim that any OS is "Better" than Mac OS X is laughable.