The real failure in the Polk evaluation was not his physical abilities but not being able to determine that the kid simply did not like to play football enough to endure the kind of mental commitment needed to play the marathon that is an NFL season. You HAVE to love the game to play at that level and he clearly didn't. He packed it in when it started to get real in the Saints training camp. Doesn't make him a bad guy, BUT it was the job of the evaluators to see through the canned answers the agents teach these kids to say in their interviews.
But the truth is, you don't always know. If it were easy then success rates on the draft wouldn't be 50%, it would be 80%. Polk was a bad pick that turned into a 6th round pick next season. Let's see what we get in that supposed "loaded" draft We've had some success in the 6th in the past. (Brady, Boutte,) who knows.