The best blocking tight end in football, and fan favorite, Mark Bruener, was released. The rest of the Steelers' tight ends (Jerame Tuman, Jay Riemersma, Matt Cushing, and Matt Kranchick) are average at best.
To be cliché, the linebackers are the heart and soul of the Steelers, and that could be a problem. Last season, Jason Gildon led this unit in sacks, and he was deemed too old to be a Steeler any longer. Haggans will be given the first opportunity to replace Gildon, but if he was really the answer, would Pittsburgh have drafted Nathaniel Adibi? Alonzo "I did NOT suit up for fourteen games" Jackson might be able to fill in for Gildon, but probably not. Meanwhile, Joey Porter has not been the same since he was shot; Joey yells a lot, but his sack production diminished greatly last season. In short, the outside linebacker position is a huge question mark.
The inside linebacker spots are a little better. James Farrior is a tackling machine, but the Kendrell Bell that we watched as a rookie seems to have disappeared. In fact, Bell has already sustained an injury and has been replaced by Larry Foote in the starting line-up (a move that could be an omen of things to come). And, heaven help us if Farrior gets injured, because Clint Kriewaldt is average at best.
The defensive line's job is to keep offensive linemen off of the linebackers. A pessimist knows that Kimo von Oelhoffen is too old, and the Aaron Smith, who earned a long-term contract a few years ago, seems to have disappeared. I tried to make sense of the following: young, talented Rodney Bailey was allowed to leave and was replaced by an older player, Travis Kirschke. Kirschke has proven about as much as Chris Hoke: nothing. Then, there is Brett Keisel, who is coming off of an injury, and Eric Taylor, who is just a rookie. In other words, Casey Hampton will be all alone on the defensive line.
The REALIST
While there will be an influx of youth and athleticism into the secondary, experience was lost. The corners and safeties are young and will get burned quite often. Hopefully, for every bad play, the secondary will make a good play (e.g. an interception) to make up for their mistakes. Optimists, pessimists, and realists all agree: Chad Scott will not be starting for long.
Realistic fans know that the offensive line is healthier than last year, but they also know that a neck injury (Marvel Smith) is a serious ailment. Plus, the Steelers will be starting two back-ups on the right side of the line: Vincent at right guard, and Ross at right tackle. Still, any line that has Alan Faneca is going to be at least above average. The entire offense depends on this unit, and the realistic fan is satisfied with, but not enamored by, the Steelers offensive line.
When Jerome Bettis and Duce Staley are healthy, they are a formidable duo. Alas, the operative word is healthy. The running game will depend on avoiding injuries, the trainers, and a little bit of luck.
Maddox has been serviceable quarterback, but he is never going to be better, nor worse, than a 20 interception and 20 touchdown type of quarterback. The Steelers were quite altruistic to give Tommy a contract extension, knowing that Roethlisberger will eventually get the reins. I say eventually, because Tommy's contract extension signifies that he will be the starter for at least this year. Meanwhile, Roethlisberger can learn on the sidelines and be ready to start once his time comes (a la Chad Pennington).

