You're kidding right? You're a PC gamer and you have no idea what Steam is?
http://en.wikipedia.org/wiki/Steam_(software)
Anyway the point is, loads of games are available on Mac now. Thanks to Steam (and Steamworks) games like Half Life 2, Counter Strike: Source, TF2, Portal and (soon) Left 4 Dead 1 and 2 and a shitload of indie games. Even WoW is available on Mac, as well as some EA Games. So yeah basically gaming is now getting a lot more popular on Macs.