See, Republicans are upset because Obama hasn't actually created global peace. Which is what the prize is awarded for. We all remember all those other people who won the prize because the world is at peace right now, right?
I wonder if the award was given because Obama took a murderous country that was despised in the eyes of the world, and managed to turn it around by ending torture, promising to close down Gitmo and end extraordinary rendition, helped assuage the global financial crisis (it's not over yet but you gotta realize things could have been worse) by the sheer fact that while being in office he's resisted the temptation to start invading other countries. In fact, he's begun talks with Israel and Palestine (which George Bush mostly ignored until the end of his presidency) and was even diplomatic towards Iran of all places when he called them on their nuclear facility.
So no, he's not perfect and he hasn't solved all of America or the worlds' problems. But unlike everyone else he's doing what he can, and he's encouraging others to do the same.