Loren Rosson has an interesting blog post on the use of the criterion of embarrassment in a discussion of the historical existence of Muhammad. For those interested in the application of such a criterion to the historical figure of Jesus (as many readers of this blog are), this post will be of great interest!
Of related interest, F. E. Peters uses some of the classic criteria in his book about Jesus and Muhammad. And there is a book about the earliest non-Muslim sources that mention Muhammad and Islam, which I am trying to remember the name of…