Left tackle is the most important position on the offensive line.
Given the rise of the 3-4 and a raft of top pass rushers playing at left defensive end (Patrick Kerney, Michael Stahan, Aaron Kampman), that just might not be true any longer. In 2008, 7 of Seattle's regular season opponents run their defense from a 3-4. Given the 3-4's ability to send a pass rusher from any spot on the line, a premiere pass blocking running back may be more important for protecting Matt Hasselbeck's blindside than a premiere pass blocking left tackle.
I've been chewing on that idea all night. It runs counter to so much I've learned, but seems airtight. Tim Ruskell's very first draft-pick of his General Managing career was a center, Chris Spencer. Centers, along with backs, are assigned with picking up free blitzers. Spencer is agile but struggles with his footwork. His lack of polish has so far negated his tremendous physical talents. The day he puts it all together, the Seahawks could have a Pro Bowler at perhaps the most important position on the offensive line.