i Have a 2010 11inch Macbook air, 100gb for OSX and 20gb for windows 7 64 bit, with my steam folder on an external HDD (as the game files are huge and space is limited).
The air i have is the base 1.4Ghz intel core 2 Duo with 2gb RAM, 128GB SSD and i can happily say it runs Skyrim fine on low settings, occasional lag if there is anything really heavy on screen, but normally fine.
I have had this Air for sometime now and is still amazes me at what it can handle. I have Team Fortress 2 running smoothly at medium settings, high textures, Red Alert 3, Resident Evil 5 runs at a smooth 30FPS, dungeon defenders runs really well on high settings (resolution 1366 x768, Vsync on)
Modern warfare 2 multiplayer is smooth, Bioshock, Assasins creed Brotherhood (playable but can lag badly for a few seconds here and there)... the list goes on. Wouldnt swap it for the new one at all....
You will be more than fine on your macbook Air, lets not forget that most games do not utilise all the RAM you have, Skyrim was locked out at 2gb (as are a lot of games) when it was released... dont believe me? Google it!
Have fun