FootballOutsiders.com has wonderful stats going back at least a decade on various aspects of each NFL team. They have a section in their stats section on offensive lines, in which they analyze effectiveness of the line in run blocking and pass protection. You can visit the site to read the details on the methodology, but it seems pretty sound to me. The interesting thing I found is that, as bad as the current offensive line is playing, its rank in both run and pass blocking is essentially the same as it was in all of 2008. That year, the o-line ranked 24 in run blocking and 29 in pass protection, whereas this year (through 14 games) it ranks 25 and 30. This means that if Pittsburgh were to win the SB, the offensive line that delivers the 7th Lombardi trophy would be only very marginally worse than the historically worst one to win it--the one from two years ago.
The other interesting thing I discovered is that the line has been terrible at pass protection for as long as Big Ben has been QB. I looked at was how the line performed going back far into FootballOutsider stats and found that in the late 90's the Steelers were pretty good at run blocking and middling at pass protection. By 2002, they were still in the top ten in run blocking and a little above #20 in pass protection. By 2004, however, Ben's second year in the league, they had dropped to 28 in pass protection and run blocking had fallen to the high teens as well. I do believe that the quality of the line declined over time as top picks were replaced with lower picks, and this is reflected in the gradual deteriation of th Steelers' run blocking rankings over the course of the decade. However, the pass protection stats absolutely plummeted over a relatively short period of time. This is less likely related to personnel on the line, in my opinion, as it is related to Big Ben taking over as QB.
As we all know, Big Ben likes to hold onto the ball, making even a good line look average and an average line (which Pittsburgh had as he entered the league) look poor. I've known that this is an issue, but I hadn't realized how clearly you can see it in the stats.
To be sure, the line quality is bad due to injuries this year and drafting neglect or failure over time, and I use the gradually declining run blocking stats as the proxy for and proof of this. However, the dramatic and sudden fall in pass blocking rankings I blame on Big Ben.
What this seems to mean is that Big Ben might make even the Colts or Pats' lines look bad. It also means that the Pittsburgh line might actually play better if Manning or Brady were behind it.