Considering that later in the game it runs like crap on my Windows gaming machine (8GB RAM, quad core 2.66GHz overclocked to 3.2, dual GTX 460s in SLI)... I really doubt it's going to be any fun playing it on a MBA.
I've come to terms with having to play Civ 5 on my maxed out machine and now use my 11" Air for occasional WoW and Starcraft 2.
Runs like crap on that rig? Something's wrong.
I'm running a quad core Phenom II + single GTX 460 + 4GB DDR3 and I play it smoothly with every single setting at max. Played two games from start to finish without a single hiccup, missing/slow-to-load texture, etc.
I'm grabbing a MBA 11" base and hoping to some gaming at my in-laws over the holiday (will definitely need some alone time...).