So far, the only coach know who has actually turned down an interview is Schott. There's an article in this morning's Buf News about why, and I believe that it doesn't have much to do with the Bills.
Rivera has only stated that he won't interview until after the playoffs, which is the same thing Grimm has said.
http://www.chicagobreakingsports.com/2010/...o-interview.htm
If we interviewed Harbaugh and decided not to hire him, it makes sense for it to be a secret, since it would have negative effects on his recruiting. If he interviewed and decided not to take it because he loves Stanford, we probably would have heard that from him, because it increases his profile to potential recruits.