A fella I work with installs his ext. wall sheathing (OSB) with the smooth side out (the grade stamp side out). I've always done it the rough side and nail lines out. His theory is that the smooth side has a wax coating that sheds water more effectively. I say hogwash. Even if it did, the housewrap or tar paper, not to mention the finished siding is supposed to keep the water away from the wall structure anyway. We've had some pretty good discussions, but we can't convince each other.
Bottom line, is there anyone else who installs OSB smooth side out, and what is the reasoning?