Nobel prizes are supposed to go to people who prove the mettle and not people may end up doing so. Winner is selected for proven record not for who is going to prove (no one knows whether a person can be proven in future).
Imagine a science nobel prize for a scientist who wants to achieve/discover something but practically hasn't achieved/discovered it yet.
Obama himself has stated that he will accept the award as "Call to Action" which means he has not acted yet. The one thing that bothers is that the nomination being made just few days after he took office as pointed by Anitha. The nominations for this year's peace prize closed ten days after he was sworn in. What the committee found worthy in ten days of office to award this prize remains a question.
While Obama may prove himself a worthy recipient (at least he has been making the right noises so far), he does not have enough actions, contributions or results to receive the Nobel Peace Prize. And that is the basis of this Prize.
This is like giving someone an 'A' in an exam because it looks like they studied/prepared well and they said so too that they will do well, but before they took the exam.

One has to wait and see how the person performed in the exam before you give the marks!!!