Joking aside, it's a very nice little machine, but I could not imagine developing software on it without hooking it up to a full sized keyboard and screen which would defeat most of the purpose of owning one in the first place.
The mac Air series is so thin that when I saw one the first time I couldn't believe it was a real functional computer until they turned it on for me!
I remember a number of times being attracted to the ultra-portable Fujitsus and Sonys of the world a few years ago and being totally unable to type effectively on them because the keys were so close together that my fingers kept getting in the way of each other when typing.
Personally, I loved the keyboard on my T23 Thinkpad.
[1] Since it's a first-gen metallic unibody, it's technically a Macbook, but they now call this machine a Macbook Pro.
The size of the keyboard has never been an issue for me, IMHO it comes down to screen real estate -- which is why my last machine isn't a MacBook at all, but an iMac 27" (my iPad provides most of the portability I need).