That's the question Claudia Rosset asks in Commentary. The short answer: pretty damn corrupt. After running through various scandals and such, she gets to a more-general point about the group:
The founding purpose of the UN was to bring peace and prosperity to the globe. As to the former, the UN in the age of terror has been in most ways useless and in some ways positively dangerous. The lesson that Saddam Hussein quickly grasped was that the UN lends itself to money-laundering. With its big flows of funds across borders, its many contractors and public-private partnerships, its gigantic bureaucracy and lax controls, its diplomatic immunity, and its culture of impunity, the UN operation is a prime candidate not only for graft but, as Charles Duelfer discovered, for arms deals masked as medicine and soap. Further protecting those arms deals, and the rogues and tyrants making them, is the fact that in its capacity as a deliberative body, the UN has repeatedly urged appeasement in the face of real threats to world peace and just as repeatedly tried to constrain those (like the U.S. and its allies) willing to act to remove them.
In the U.N.'s favor–and this is no small point–you'll recall that last year the group (via Unicef) produced an anti-war cartoon in which the Smurfs are literally bombed back to Belgium or whatever Fourth World hellhole from which they sprout like so much fungus. More on that delightful scenario here. Here's looking forward to a U.N.-approved "Tin-Tin in Abu Ghraib" cartoon next.