Nebraska's pass defense lost an important piece in 2011 when Prince Amukamara made his way to the NFL draft, where he was selected in the first round by the New York Giants. I think they had a good year. The onus to fill the shutdown corner role fell to senior Alfonzo Dennard, and Dennard did not disappoint.
Almost everything Amukamara brought to the table, Dennard does too; he's physical, has excellent ball instincts and can generally keep coverage on deep routes and fades without getting torched.
The one difference between the two players is that Dennard isn't quite as skilled when he's asked to play off the ball and give an opposing receiver a free release downfield. He's susceptible to double moves out of this position and was routinely beaten in the Senior Bowl when he wasn't up on the line. This probably has as much to do with unfamiliarity as anything, but GMs usually don't want to draft work-in-progress cornerbacks in the first round.
To be sure, Dennard's top-level speed isn't the best, and that only reinforces why he's generally a high-level second-round pick (if the Vikings let him go past 35, they're insane). That all said, being fast is all fine and good for a cornerback, but the real job of a cornerback isn't to be fast, it's just to be faster than the guy you're covering. The guy you're lining up against might be an all-world sprinter who runs a 4.2, but if he can't get around a 4.5 cornerback who's got superior physicality and hip swivel, then that wideout's not really a 4.2 guy anymore, is he?
So that's why I'm not terribly worried about Dennard and what his sprint times look like. He proved time and time again during the 2011 season that he can be counted on to shut down the best receiver on the other team, and as long as his new coaches use him to the best of his strengths, he'll be just fine at the next level.