A lot of the mock drafts that I've seen around the web have us selecting a nose tackle or defensive back to fill an immediate need.
However, when you look at the grand scheme of things, we usually don't draft rookies with the intent of starting them the same year. So, in reality, there wouldn't be too much of a point drafting a Terrence Cody or a Taylor Mays (not that I want the Steelers to draft him, but you know what I mean) because the Steelers defense is just too hard for a rookie to handle. When you look back at Troy Polamalu's rookie year, he looked completely lost in the defensive backfield, and look at how's he's developed. The FO has seemed to address needs that will APPEAR IN THE FUTURE, not the ones hurting us in the present time.
Because of all that, I don't think the FO will let Casey Hampton, Ryan Clark, and Willie Parker all leave at the same time. Rather, I think at least two of the three will stay on the team, most likely Ryan Clark and FWP. And if we do indeed draft a NT, dont' expect for him to see a lot of playing time. After all, the Packers drafted BJ Raji with the 10th overall pick, and they had a MUCh greater need for a DT then we do this year. I wouldn't be surprised if we do let Big Snack walk to see a free-agent DT come in to fill in as a stop-gap so that the rookie can learn for a year or two.
On top of all that, though I don't have the exact number, it's been a long time since the Steelers drafted two positions in the first round back to back. Last year, they drafted Ziggy Hood, thus taking care of the defensive line. I don't think the defensive line is big enough of a problem to warrant two consecutive first-round picks. Rather, I wouldn't be surprised to see the Steelers try to make a move to draft Rolando McClain, especially since Farrior hasn't exactly been playing his A-game towards the late stretch of the year.
My thoughts on draft day?
I think we'll go LB, RB, FS, DL, and then the rest BPA.
My favorite players for the first three rounds: Rolando McClain (hoping he falls because Denver takes a QB or WR), Jahvid Best (his injury history won't help his draft stock, and he'll be an amazing 'back once he gets used to the pro game), and Myron Rolle out of FSU (Sure he hasn't played football in a year, but he's an amazing safety, and plus, he's insanely smart as well [was awarded the Rhodes Scholarship, which is why he didn't play for a year] He'll definately be able to pick up LeBeau's scheme pretty quickly)
On a side note, our draft needs could very well change if we get a new offensive coordinatory. In fact, if we get the off. coordinator that pounds the ball 30+ times a game, we might even take a fullback in the first round!