I don't have a lot to offer that hasn't been said yet, but thought I would at least add a perspective from someone who has seen him play. We live in Kentucky, and one of our homes is in a Louisville suburb. I get up there from time to time and catch a game, and I really like this kid. I agree that the injury may have been just enough to keep him below the horizon for a lot of teams, or he would have gone earlier. Here are the pluses and minuses, the way I see it...
He has NFL-level speed and ball instincts right now, plus very fluid hips and an excellent change-of-direction. The downside is that when I've seen him, he seems to rely on his speed to make up for occasional poor coverage decisions - that won't work as well at this level. I think that's also a reason that he's better at defending intermediate or deep routes - his coverage is not as effective on short passes, and I think it's because he doesn't have the time to use his speed.
He's a scrapper when he has a shot at stealing a ball or breaking up a pass, but not physically aggressive when tackling. His run support is weak, and he doesn't tackle well in the open field. He's not going to tattoo many receivers. I think that's because his build is very slim, and he just shies away from really hard physical contact. He also uses his hands way too much; coaches are going to be all over him in training camp on that one.
One thing I haven't seen mentioned here is his attitude - which is a little surprising, since he certainly has one. He's a very cocky kid, but in a good way, a matter-of-fact way. He's extremely confident in his abilities. He's said many times here in the local media that he's the best DB in the draft, and openly boasts of being the best shutdown corner in college football. And the tape bears that out - he basically took away his entire half of the field from every quarterback they faced this season. Opposing QBs had a passer rating of just 17.7 when throwing at him. Part of that is probably the way he has of getting inside the receivers' and the quarterbacks' heads - he's a pure, loudmouthed trashtalker, and drives receivers and quarterbacks straight-up nuts.
Short version is, his basic skills are exceptional, and most of his weaknesses are coachable - and keep in mind, he'll be the youngest player on the team. He came out a year early. Other than his size and his frame, just about every weakness is coachable, and he has a good reputation here for coachability. I imagine he'll be carrying another 10 pounds or so by August, but he's never going to be a Nick Collins in the secondary. You're not going to see many highlight reel, knock-the-helmet-off tackles from him. But you should get a solid, shutdown cornerback with blinding speed, super-glue hands, and a chance for a pick-6 2 or 3 times each game.