Kevin Colbert is known as one of the best at his job in the NFL. The Steelers rarely miss on picks in the first 3 rounds. Virtually every player taken in those rounds since Mike Tomlin became Head Coach are either starting or make regular contributions to the team.
I find it hard to actually consider any of the players drafted after the 4th round "bad" because they are after all normally considered value picks. Their chances of making the team at all greatly diminish the further down the draft chart you go. Still though there are some that have been solid late round choices.
In random order:
David Johnson - 7th Round 2009 - Johnson is a regular on offense especially in short yardage and goal line situations. He's a good blocker with underrated hands.
Ryan Mundy - 6th Round 2008 - Mundy has fought through injuries to be a decent option at reserve Safety. I was worried when he was in for Polamalu late in the year but I have to tell you he did pretty well considering the shoes he was filling.
Dennis Dixon - 5th Round 2008 - Had Dixon not gotten injured last year he would have been the starter for all 4 games when Ben was out. He has improved his passing skills during his time in Pittsburgh, but his best asset is his scrambling ability which has allowed him to keep the chains moving many times.
Antonio Brown - 6th Round 2010 - Brown has solidified the Steelers return game in 2010 and his circus catches have been something to behold. He was instrumental in the Steelers playoffs wins against Baltimore and the New York Jets. He's got great speed and a nose for the football.
Crezdon Butler - 5th Round 2010 - Butler will get his chance to compete for the 3rd CB spot in 2011, I'd be willing to bet on it. I think he's got a big upside and will challenge Gay for his position.
Stevenson Sylvester - 5th Round 2010 - Like Butler, Sylvester has a big upside and at this point seems to be the heir apparent to James Farrior. While he's still unproven I've definitely liked what I've seen from Sylvester and in my opinion should get some considerable reps this coming season while spelling Farrior. Not that Potsie needs it but the Steelers should start getting there young prospect some more experience.