According to Daniel Jeremiah of MoveTheSticks.com, Okung weighed in at 307 pounds and stood 6'5" with 36" arms.
Those are very long arms, which is a good thing. Offensive tackles with short arms, as Jeremiah points out, can allow defenders to get into their chest and gain leverage, which is a "major problem."
33" seems to be the minimum a lot of these guys are shooting for.
A little background on Okung in case you've been living under an Arrowhead the past few weeks and months. He's rated by many as the top tackle in the 2010 NFL Draft. He's also the one many a mock drafts have the Chiefs taking with the 5th overall pick.