The zenbook has a 1.7 GHz processor. Most ultrabooks have processors with speeds 1.5 to 1.8GHz, which might not be the best for development. A T430 with SSD would be a much more compelling dev laptop.
It looks like the T430's best resolution is 1600x900. The ZenBook is 1920x1080, 1.44 times as many pixels. This is the main reason I'm thinking about getting the ZenBook.
I have a Zenbook and love it. Would recommend the UX32VD over the UX31, as you can upgrade the SSD and the RAM. (Jeff Atwood actually uses the UX32VD - he gave the UX31 to his wife.)