There is an interesting article in the Journal of Strength and Conditioning Research for Nov., 2008 entitled "The NFL Combine: Does It Predict Performance in the National Football League?".
In it the authors state, "Using correlation analysis, we find no consistent statistical relationship between combine tests and professional football performance (of quarterbacks, running backs, and wide receivers), with the notable exception of sprint tests for running backs."
"Given the substantial gap between the skills assessed at the combine vs. the skills ACTUALLY REQUIRED TO SUCCESSFULLY COMPETE AT THE PROFESSIONAL FOOTBALL LEVEL, the lack of relationship between the combine performancve and NFL performance is, therefore, not surprising."
The finding of no relationship between the combine tests performances and NFL success as a wide receiver is contrary to the opinions of "draft gurus" and may explain why there are so many black WRs who are not good, but given preference over white WRs (who can actually catch the ball). It can also explain why "unathletic" white QBs outperform the "superior athlete" black QBs.