To celebrate the launch of Steam for Mac and their upcoming sequel to the award winning FPS puzzle game, Valve is giving away Portal to anyone (Mac or PC) between now and May 24th.  If you haven't already downloaded the steam client, head on over to Steam and download it while you can.  Thanks to SteamPlay, once you've downloaded it on your Mac or PC, you're free to play it on the other.  What are you waiting for?  Go get it while you can!