If you're okay with it, I'd actually suggest buying a MacBook Air and running Linux on it. My experience in the rest of the "ultrabook" world is that they just weigh far too much.
On the flip side, I'm also using a System76, which I've come to love. If you're interested, I wrote a review on my blog (http://www.lyricalsoftware.com/blog/system76-galago-review/)