I have the 2.4GHz MacBook and have so far had the chance to play both WoW and Spore on it. As a really quick summary: if you have an iMac or a MacBook Pro from around 2006 (the versions with an ATI Radeon x1600), the gaming performance is roughly equal. I should know, I'm typing on just such an iMac and have likewise played both WoW and Spore on it.
WoW is fully playable and runs at or near 60 fps at 1280x800 with medium visual settings. I run the game with generally medium-to-high settings (texture and model detail on high, draw distance about three-quarters to maximum (remember that they increased the max draw distance in 3.0), spell effects on medium, glow effect off, etc) and get about 30-60 fps. This is a drastic improvement over the older MacBook that I'm replacing, which had an Intel GMA 950 and would cry horribly even with all visual settings reduced to near-minimum.
Spore is likewise quite playable. I don't know exactly what framerate I'm getting, but it feels like it's in the 40-60 fps range, and I'm running it at 1280x800 with more or less medium graphics settings.
While I have yet to install Windows on my MacBook and subsequently try Source games like Half-Life 2, Counter-Strike: Source or Team Fortress 2, given the similar performance to my iMac I feel comfortable saying you will probably be able to play the older Source games with settings pretty much maxed out, and the newer Source games (including TF2 and Half-Life 2: Episode 2) at medium settings.
I hope that helps some people out. This machine has been surprising me at just how good its gaming performance is.