Also check out F For Fake - http://www.criterion.com/asp/release.asp?id=288 - the film Orson Welles made. It deals with art forger Elmyr De Hory, who Clifford Irving wrote the biography of before he got the idea to do his Hughes book. It deals with the Irving Hughes scandal and various other notions of fakery.

The extra features on the DVD are good too, including a 60 minutes interview with Irving and the telephone interview Hughes was forced to do to defend himself against the claims made in the book.