That, at least, is the word down from Pro Football Focus. They came up with an ingenious if seemingly random formula to distill pass blocking into one handy number:
((Sacks + (0.75 * Hits) + (0.75 * Hurries)) / Pass Pro Snaps) * 100
They then ranked every tackle with at least 200 pass protection snaps, which is generally about one third of a team's total pass snaps. The fifth worst right tackle on their list is Jeremy Trueblood. That's hardly a surprise to anyone reading this site, I've been ranting about Trueblood's inability to pass block for a while now. This is only more validation of that simple fact.
More surprisingly, Donald Penn was listed as the 7th worst left tackle in the NFL. That's pretty counter-intuitive, as Donald Penn not only made a Pro Bowl but was universally praised for his pass blocking. So I went back to Football Outsiders' charting data to see how he did. He blew 20 blocks leading to hurries or sacks, while Trueblood blew 17. But if we factor in the amount of snaps they played, Penn did 37% better than Trueblood according to Outsiders' data, while he only did 13% better according to Pro Football Focus's. Having done much of the charting for Football Outsiders', I'm more inclined to believe their data, if only because I'm familiar with the process.
There are a few mitigating factors for Penn, though. He went up against some pretty good pass rushers like John Abraham (twice), Terrell Suggs, Brian Orakpo and Will Smith(twice). He had little trouble handling any of the other pass rushers. Because of the poor state of the rest of the offensive line he was often isolated against one, or trying to block two pass rushers. But a premier left tackle in the NFL should be able to handle those players and those circumstances. I've been an advocate of Penn this past season, and I certainly don't think he's the 7th worst pass-blocking tackle in the league. More likely he's about league average, perhaps a bit better, and a small sample size plagues the big man's numbers.
As a run-blocker, though, Penn may be more valuable, and when he gets in space as a blocker on screens he is devastating. The Bucs did give Penn a big contract before the 2010 season, but it wasn't a premier contract. He got second- or third-tier left tackle money, which seems about right to me. And the Bucs don't need to spend more on their left tackle. Protection schemes have evolved to the point where a quarterback can compensate for mediocre tackles, as long as the interior of the offensive line is competent. And that's where the Bucs need to improve most.