Blitz started reviewing every Steelers player by position, so I'll help him out a bit and do the DB's. I don't have YPA numbers for these guys, so if someone wanted to add those for the starters, that would be cool.
Taylor has been solid at CB. I'm pretty sure he's only been beaten deep once (sadly by a white former college QB), which resulted in an odd but probably correct PI call. Ike is very good at staying with WR's in coverage, but not always great at playing the ball if QB's challenge him, and this year is about par for him. Teams have not challenged him a whole lot this year, so it's hard to judge his overall performance. He has yet to record a deflected pass or an interception in 5 games, which is incredible for a starting CB who isn't terrible.
It's difficult to say if McFadden is benefitting from playing full time or if he truly took a step forward this offseason, but he looks like a different player. When he came in during nickel situations last year, he looked passive. In the games he's played so far, he's been the Steelers best CB. I doubt McFadden is quite the athlete Ike is, but this year he's playing the ball as well as any Steeler corner I've seen since Woodson. It's still early in the season, so it's possible opposing teams will adjust some to him and find a weakness (maybe double moves?), but so far it's been great to have a playmaker at CB.
Coming off his best year as a pro in 2007, Townsend has had some injuries and been a little disappointing so far this year. When McFadden started playing well, I was excited to see the 2007 version of Townsend come back into the lineup as a nickel back, but when crunch time came against Baltimore, he gave up a big pass play and missed the tackle that put the Ravens inside the 10. He could still be affected by the injury, but if he doesn't look more like 2007 Deshea before the end of the season, I'll be even more nervous about letting McFadden walk at the end of the season.
There are two types of safeties that get recognition in the NFL: hard hitting, blow-up-the-runner strong safeties, and ball-hawking free safeties. So far in 2008, Polamalu has been the superhuman combination of those two. We know the story: after earning his hype in 2004 and 2005, he fought injuries, flew past ball carriers, and got beat in coverage in 2006 and 2007. Well, I would say he's back, but that doesn't do him justice. So far this season, he's broken up numerous deep passes, made 3 interceptions including maybe the most acrobatic catch I've ever seen, thrown TE's into the backfield on running plays, flown to the ball on screen plays and MADE THE TACKLE, showed incredible range, limited Kellen Winslow while covering him for a whole game, tackled a guy behind his back, and jumped over the offensive line. He's one of the best run defenders on our team, and he might be the best pass defender as well. I don't know how he could be anything other than the most versitile player in the NFL and the defensive player of the year if he keeps playing like this. Some of his best competition for DPOY will probably come from Harrison and Woodley.
Clark has gone from being solid but unexciting to desperately missed to back towards solid but unexciting. He's played more in run support than in years past, and he's looked good doing it. He has a couple of nice pass breakups, but missed a read and was the primary perpetrator on a fairly long TD pass against the Jags. He hasn't stood out much, good or bad, which is fine. We need a solid guy who won't make huge mental mistakes, and that's what we have in him.
William Gay/Anthony Madison/Tyrone Carter/Anthony Smith
I haven't seen these guys on the field much on defense, but a couple have really made their presence felt on special teams. Madison in particular has been a force on the coverage units recently. Gay may have gotten the most playing time of the bunch, and he didn't look like a liability in nickel packages against the Browns.