I read this article quite a while ago.  It is filled with hilarious draft day stories.  If you have 5 minutes you should read it.  There is a story in there about how the Cowboys got Ditka.

Here is one example in the article:

The Redskins made UCLA running back Cal Rossi the ninth overall selection in the 1946 draft before realizing that he was coming off his junior season and wasn't eligible. The persistent franchise once again drafted Rossi in the first round of the 1947 draft. The only problem was that Rossi had made it known he had no intention of playing professional football, and true to his word, he never played a down for the Redskins.

Let's fast foward 49 years.

Projected as a first-day pick in 1995, BYU offensive tackle Eli Herring wrote letters to every team in the league indicating he didn't intend to play because of his religious beliefs.

The Raiders gambled that the devout Mormon would eventually change his mind and selected him in the sixth round.

http://sports.espn.go.com/nfl/draft07/news/story?id=2835262