Using an Air as your main development machine seems odd to me - I want a large display so that I can read docs/papers and have emacs open at the same time. I also want good separation between screen and keyboard for maintaining decent posture. I hate to use a laptop as my main machine for exactly that reason. My main development machine doesn't get picked up and moved around enough (at all?) to be worth using a high end laptop. For the same price as the machine at the top of the page you could buy a decent desktop and a 13" Macbook and lunch, I guess.