I think that, perhaps, they were not just looking at the two weeks he had in office (and, I think, that though the nominations were in, the voting came later in the year? Although I could be wrong). The reference to his "bringing together" of people could refer to the year long presidential campaign, a bit. Although it was largely America-centric, the rhetoric he used and the emotions he inspired had world-wide implications. Granted, he hasn't (besides getting rid of the missle defense in Europe business) necessarily got a lot of concrete accomplishments to point to, but I believe that this award was at least partially about inspiring others and changing international discourse.
Whether that is enough to deserve the Nobel Peace Prize, I'm not sure, but I do think that a lot of this was about how the discourse was changed and what that could mean for the world as a whole. At least for my family, it wasn't that long ago when we were talking about "when" Bush was going to invade Iran, not "if". Now, it feels like a step has been taken away from war?
Sorry so dis-organized.