Jamarcus Russell is a bust but I just don't know that many sources who thought he was going to be good in the first place. When he came into the draft it was pretty much accepted that his physical skills were going to make him a number one overall, but I don't recall anybody really believing that those physical skills alone were going to make him a successful QB because there is so much more.
For me, a truly monumental bust is somebody that everyone thought was going to be really good and turned out not to be. Nobody that I can remember really thought that about Jamarcus Russell. I wasn't paying too much attention when the Leaf/Manning thing was going on and whether or not a lot of people really thought he was going to be good, but the fact that Leaf will forever be foiled by one of the greatest QB's of all time has to be a big part of why he is seen as such a huge bust.