I've had good luck with FreeBSD on Lenovos. Its run on every one I've had since my T42 (so T42, R60, T500, T510, T520). Power management works "fine", I usually get 5-6 hours of battery life out of my battery, but I never bothered to monkey with suspend/resume since my laptop boots so fast anyways.

Frankly the Air is one of the best laptop formfactors I've seen in a while, just load a virtualization system on it (VBox is free) and run FreeBSD in that.