There are quite a few very good 64bit *nixes around, you know? What's keeping you from using them, and if it's gaming and Microsoft programs, why not setting up a dual boot machine?
/agree. Ubuntu is freaking incredible. You can do everything you could in Unix + X11, plus you have access to all the source code, plus Compiz will give you eye candy that shames Aero and Mac. I use it for pretty much everything except MS Office and games (for which I use XP).
I did consider it for a while, but there is little of the stuff I use that comes in *nix flavours (a few of them come in Mac versions but that is about it). It is going to be used for both play and work.