Performance-wise the Pro is no different than the MBA or any other ultrabook, so it all comes down to the form factor. For portable (especially lap) use the combination of kickstand + type cover makes typing a bit more difficult than a normal laptop, but on a desk it works pretty well. There are two caveats though: the relatively small screen and fixed kickstand angles (now there are two different angles but obviously still not as flexible as a notebook).
It only makes sense if you expect to use the tablet/touch features a lot, in addition to the traditional desktop. I plan on getting one mainly for the digitizer to take notes, so having a full portable computer is a nice bonus and justifies the price since I currently don't have a notebook.
I hear great things about the Pro. You would definitely not want the RT/ARM models as a developer. Whether you want to spend $900+ on the Surface Pro to use a dev machine is another matter.
the touch cover is not that great but the type cover is awesome for typing. Looks like the second version of it is backlit as well so it does make for a great dev PC
I totally agree with you. The touch cover is useless. I haven't got a chance to try the type cover yet, but I assume it to much tolerable than the touch cover. The only complaint, it doesn't come in colors :(
