Why hath this not been posted yet?
So, epic news, if you haven't heard: Valve is bringing Steam to the Mac
, starting with Portal 2 (which just seems to fit). The great part about it is that you can save/quit a game on PC and then continue playing on the Mac, and vise-versa. Rather than Steam only sticking to either Mac or PC with no functionality between. So, ultimately, PC users can battle Mac users. Which should be terrifying, given the war between PCs and Macs.
I really love that Valve did this. You don't see many other companies who are willing to accommodate other platforms, especially Macs. It shows that they're truly devoted to the players. Maybe this'll put Macs into the gaming category now. Who knows.