Another breathability question

On a few occasions I have sorta soaked a shirt when layered as Chad has described. It's never bothered me, though, because I figure if I'm sweating that much I'm plenty warm. If I'm going to stop for a while, I throw on an insulating or wind layer, let body heat dry the base, and stay warm. But back to the OP, the most common mistake I see people make is wearing too much clothing just because it's cold outside… you want to be a little cool at all times, particularly on the move.