I just got my Air today. 1.6/4gb. It's a very nice, snappy machine. However, I'm a dissapointed in the gaming performance. Mostly because people on the forums, obviously not gamers, are overstating the performance.
On Starcraft 2, native res, everything on low, you can expect around 22-25 frames per second. With everything on low except for shaders on medium (changes the way the game looks completely, much better), you should get around 14-20 frames per second. This is on the last level in the single player campaign. I used that for testing cause you start out with a lot of units and stuff going on in the screen.
Playing it at a non-native res might boost the frames per second a tiny bit, but it's unplayable. The screen is very nice at native res, but at ANY res that's not native, it becomes VERY blurry. So blurry that any text on the screen is near-unreadable. So... it's not recommended to use a non-native res.
World of Warcraft fares better, I didn't check actual FPS numbers yet, but it seems to run at around 25-30 fps with everything on "good", and I'd guess between 50 and 60 fps with everything on "fair" (low). It's perfectly playable, and much more enjoyable than Starcraft. (I found Starcraft to be playable, but not very enjoyable).
I hope Diablo 3 runs ok on this once it comes out, if not, I might ahve to upgrade earlier than I was planning to...🙁
Besides that though, it's a very nice machine 😉