This year, there is a plethora of top defensive players across the front seven. There is no question that the talent in this year's class is top-notch.
With that said, there have to be players falling far from where they are projected to go. Every year a top player falls. It does not necessarily mean they are bad players. Needs and questions about injuries/character issues are the main reasons for slips.
Look at Aaron Rodgers. Many teams passed on him, mostly due to his character, and teams did not want to take a risk with a quarterback that may have a sort of "cockiness" to him. He took a few years under Brett Favre, studying how to act and how not to act. Now he is the MVP of Super Bowl XLV.
I am not saying that these players are not going to be good. I am clearly saying that questions do arise and will make a player, such as Da'Quan Bowers, fall past the 20th overall pick.
Here is my first mock draft of the 2011 season.