My problem with Dell is that their keyboards usually suck. They are not that bad, but certainly worse than ThinkPads and MacBooks. Also, this actual model is more expensive than the Chromebook Pixel, and is arguably worse at every detail (except for the bigger SSD).

Portability goes a long way, and iirc it's a smaller form factor.

That said, I'm not sure that I'd choose it over the pixel either.

No NVIDIA or ATI card? How is the graphics performance?

After my current experiences running linux on a laptop with an optimus enabled graphics card I can safely say that I am never again going to buy a laptop with discrete graphics to run linux. It's been a pain getting Bumblebee to work (optimus drivers), and even with it working certain parts of the hardware are still closed off, thanks to limited driver support.

Not sure. I haven't seen one in the flesh, but I've heard good things about it. Nothing first, or even second hand though.

Personally, I wouldn't buy an ultrabook for the graphics performance, cooling is just too problematic to do anything overly shiny in my view, but I can't imagine you'd have issues running a shiny window manager or decoding 1080p video, which is the two most graphics intensive tasks I do.