From Youtube: Interview with Bart Ehrman about Forged.
I know I gave the actual book a mixed review, but this radio interview does a better job of hitting what is really of interest about the issue.

....On a related note: one of the thing that Bart Ehrman stresses both in his book and in the radio interview is that there is very little debate among scholars that much of the New Testament is under false names.  Mainstream Catholic and Protestant Universities also teach that Peter and Paul couldn't have possibly have written many of the letters claiming to be from Peter and Paul.  The only debate is whether this constitutes outright forgery (as Ehrman claims) or whether it was simply just an accepted ancient practice (as many Christian seminaries claim).
This was my own experience as well--at Calvin College (a conservative protestant school) I was taught that some of the letters of Paul and Peter were written by other people under false names.   This was shocking to me at the time, but interestingly enough it turns out, according to this article  here, that John Calvin himself thought that 2nd Peter couldn't possibly have been written by the apostle Peter--or at the very least that Peter couldn't possibly have written it directly himself.  So I guess it should be no surprise that Calvin College taught the same thing.
John Calvin thought that the letter must have been written at least under the direction of Peter because:
If it be received as canonical, we must allow Peter to be the author, since it has his name inscribed, and he also testifies that he had lived with Christ: and it would have been a fiction unworthy of a minister of Christ, to have personated another individual. So then I conclude, that if the Epistle be deemed worthy of credit, it must have proceeded from Peter; not that he himself wrote it, but that some one of his disciples set forth in writing, by his command, those things which the necessity of the times required.

 If I'm following John Calvin's logic correctly, he thinks that  because the book is canonical, it must be inspired by God.  And because it is inspired by God, it can not contain a falsehood.  The fact that the author not only claimed to be Peter, but claimed to have lived with Christ, is a falsehood unworthy of Christianity, therefore the letter can not have been a complete forgery, but must have been written under Peter's direction even if he didn't write it directly himself.
Of course there's no evidence that the letter was written under Peter's direction--that's just wishful thinking on John Calvin's part.  (And indeed, many of the problems with 2nd Peter--that it copies from the letter of Jude, and that it refers to the apostolic age as something in the past--are not solved by this explanation).   But I think Calvin's framing of the problem still stands.  If the letter is forged under Peter's name by a different author, then this is a falsehood unworthy of a minister of Christ.