I've been looking at ultrabooks capable of running Linux these last few days and Dell's XPS 13 Developer Edition seems like a pretty nice package.
Some articles with useful information about the machine and the out-of-the-box experience:
Divorcing Apple, trying WIndows 7 and Ubuntu on Dell XPS 13 Ultrabook
Back On Linux – Dell XPS 13 Developer Edition
My Review of the Dell XPS 13 Developer Edition (a.k.a. Sputnik)
Putting Dell's Ubuntu Ultrabook to the test