I'm usually no big cheerleader for corporations, but this is one time where my interests are intersecting in such a way that I can't ignore it.
Valve (makers of Half Life, Team Fortress, Left 4 Dead, and Portal) are bringing their games to the Mac. This alone would be very good news. But it gets better.
They're also bringing their online store Steam (think iTunes but instead of music it's face-melting video games) which will encourage other gaming companies to start getting on the ball with their own Mac versions. They're also doing something kind of unprecedented. If you've already bought the game on PC, they're going to allow you to download it on your Mac. And to cap it off? They're going to have cross platform multiplayer, so PCs and Macs can play together.
Valve games constitute about 75% of all PC games I play. Today's news is that I might never buy another Windows machine again.