Well, I'm glad you asked.
First off, he's done an excellent job representing our president at the UN. He may not have gotten as much reform as he would have liked, but that's a tough nut to crack. Plus, since everyone watches American politics, especially foreign diplomats, everyone knew he didn't have the full support of congress. That made it easier to ignore his inconvenient truths. (heh, I made a funny pun.)
It will be a long time before we have such an effective representative of our country, and I hope one day to be as successful at that job (representing his president) as he was.
Too bad, that's what I think about the resignation.