To everyone who is asking why anyone would buy one of these, or why Intel is pushing the concept, the answer is the success of the MacBook Air.
The MacBook Air has become mainstream, and is selling like hotcakes. Intel doesn't want to be beholden to Apple to sell its lucrative ULV processor line. Apple has already spurned Motorola (in 1994 with the switch to PowerPC) and IBM (in 2006 with the switch to Intel), and could easily do it again if ARM or AMD chips become powerful enough for them.
However, if the "Ultrabook" takes off, Intel will have a lot of other buyers for their ULV processor line, which will help boost their bottom line, as well as give them resources to build even lower voltage CPUs that could take on ARM in the tablet/mobile device space.