wow is definitely playable on medium-ish settings, as stated previously. It's not smooth all the time though. I routinely get 10-30fps, with an average of ~20. I have a 2GHz with 1GB Ram and the GMA950. I have a 2GB stick being delivered today though, so I will let you know if that makes much of a difference.
From what I understand, you can get ~10fps more in windows than in OSX, possibly due Windows being able to allot about 3-4x as much memory to the GMA950. The new MB video is much more capable than the GMA950 too (which is still not saying a whole lot), but it should perform even better. just something to think about.
hopefully everything I said makes sense, I've been up a while