This is interesting to say the least. Check it out and check out NFL busts by percentages for years' 1989-2003. You can navigate from position to position and then to the conclusion.
http://sports.espn.go.com/espn/page2/story?page=kluck/quarterbacks/070425
http://sports.espn.go.com/espn/page2/story?page=kluck/quarterbacks/070425