If you know what Steam is and have been waiting with bated breath for its release on the Mac, today is the day. Download Steam right here in all of its new .dmg glory.
Yes, this means that you can now play Portal and Team Fortress 2 on the Macbook pro you tote around. From the whole PC gaming world, welcome to the 21st century. As a short side note, a hack might still be needed to fully access the application.
The hack (a workaround, really) can be found here. The need for this workaround will disappear shortly, by the time you read this it may not be required. If normal use fails, try the hack. If not, welcome to modern gaming on your Macintosh. Let the celebrations begin.