Jon Krakauer, an early supporter, probably summarizes this pretty well (maybe a bit more charitable than others may be willing to be) when he says,
"Krakauer: He's not Bernie Madoff. I mean, let's be clear. He has done a lot of good. He has helped thousands of school kids in Pakistan and Afghanistan....He has become perhaps the world's most effective spokesperson for girls' education in developing countries. And he deserves credit for that...Nevertheless, he is now threatening to bring it all down, to destroy all of it by this fraud and by these lies."
You can read the expose from CBS news here.
Update note (same day): Galley Cat has a summary. It also includes links to statements by Mortenson and CAI that they sent to CBS regarding the 60 Minutes segment.