As a developer, the only software I need is Zend Studio and Adobe CS, which are both available on Mac. With the increased portability and longer battery life, the Macbook air may be just the thing I need. I'm looking at the 13 inch right now, and I'm strongly considering buying it.
I also carry a lot of stuff in my bag, including a camera, a/c adaptor, and a some other computer equipment. 2 lbs doesn't seem like much but if I have to be mobile for a long period of time, it's definitely noticeable.
Would I get it? Probably not. I don't have that much expendable income to have a power laptop and a luxury netbook.
My next Mac will have a faster CPU, 8GB+ of memory to support running 1-2 VMs, and 500+ GB disk to store them. The MBA just doesn't cut it.