Most people I talked to are perplexed. Surely he hasn't done anything truly great so far, except maybe being the first non-white to win US presidential elections... but this is hardly a reason for being awarded the Nobel.
I have a different explanation, which starts eight years ago.
Even before 9/11, largely for explicitly stated ideological reasons, the Bush jr Administration had begun to systematically undermine existing international institutions by going unilateral or refusing to cooperate on such things as climate change, ballistic missiles, the International Criminal Court. American exceptionalism was not new, but seldom in history had it manifested itself in a such systematic way. After the traumatic terror attacks, the unilateralist camp gained virtually complete control in shaping America's foreign policy. It coined the so-called "Bush doctrine" that promotes the idea of preemptive war. And it put it at work in 2003 by launching a war against Irak based on (as we now know) false allegations of Saddam developing and stockpiling weapons of mass destruction and supporting Al-Qaeda, and outside international law as it failed to obtain the approval of the United Nations.
The US, clearly, was no longer willing to act with self-restraint within the existing international system, and was more than ready to flout existing norms and institutions whenever it so appeared more expedient to defend (what it considered to be) its national interests.
This type of behavior is what I described as neo-barbarian in an earlier post. Most of the world reacted with fear and horror to such vandalism, sympathy for the US dropped sharply and suddenly it started to top public opinion polls about countries that are a threat to world peace.
Incidentally, another consequence of such foreign policy was to dramatically undermine America's soft power and influence in the world. From being mostly perceived as a relatively benign superpower that largely controls the international system and has an important stake in its preservation and consolidation (remember Bush senior's talk about the "New World Order" and the very different way in which the first Irak war was conducted in 1991 within a UN-sanctioned framework), the US started to behave recklessly in pursuit of narrowly-defined national interests with no concern for the damage done to the international institutions. Ironically, all that the world superpower needed to do was to translate its national interest into the language of universal principles that others could understand and follow - but the New Barbarians were intent on precisely not doing that.
Acting like a bully, outside the rules, even when you are the strongest country in the world, has some long term costs. It makes your behavior less predictable; it makes it easier for adversaries to oppose you and justify their opposition through principles (as France opposed the Irak war, with president Chirac managing a significant surge in his moribund popularity); and it makes it more costly for your allies to follow you and be able to justify such support in front of their own public opinion (as illustrated by the severe political damage that Britain's Tony Blair and Spain's Jose Maria Aznar, who supported Bush in Irak, suffered domestically). Eventually, you end up with fewer friends and less influence.
And the world becomes a more insecure place.
Obama's promise is to bring America back into the international system. And this promise was received enthusiastically by the world, because it announces better times when the most powerful man on the planet and the most powerful country on earth will act within a system, within some limits, within the realm of civilization as opposed to barbarity.
By the mere fact of changing the direction of US foreign policy and adopting a cooperative attitude with the rest of the world, Obama has been effectively contributing to restoring the enfeebled world order. Not surprisingly, America is once again popular.
And the Nobel Committee says it explicitly in its brief justification:
Obama has as President created a new climate in international politics. Multilateral diplomacy has regained a central position, with emphasis on the role that the United Nations and other international institutions can play. Dialogue and negotiations are preferred as instruments for resolving even the most difficult international conflicts.
Now I agree that awarding him the Nobel Peace Prize is maybe too much at this point. But this is not about Obama. It's about a world that has suffered mightily under the New Barbarians and now gives a sigh of relief. And has high hopes from its new leader.