Keep in mind, he's played for some of the worst pass defenses in the NFL (2007 Det-31st, 2008 Det-27th, 2009 Jags-27th). It would be one thing if he were cut by a team with a good pass defense, but the fact he couldn't stick with the Jags says a lot.
From his stats, he looks more like a play in the box SS than a cover guy. He's started 27 games (played in 36) with a total of only 11 passes defended in 3 seasons (but also has 4 interceptions), with 111 solo tackles/143 total in those games.
Stats can be misleading, though--if he was the cream of the crop on a defense that leaked like a sieve, maybe they just didn't throw the ball his way. I haven't followed him close enough to tell the difference...