If you can live with 8GB RAM and a dual-core i5 at 1.8Ghz, I'd argue that the MBA is one of the best laptops to work with. The selling points for me are:
* OSX - still the best all around OS to work with.
* Lightweight, it is a laptop that weights ~ 3 pounds
* Battery life is decent
* Build quality is above average
I believe that it's an excellent choice for web development.