As a non-physicist (), I'd have to agree that it would have something to do with the amount of force perpendicular to the aeroplane, but then I'd imagine that some sort of adjustment would have to be made with respect to certain characteristics of the aeroplane itself - size of the vertical stabilizer, etc - that would create varying changes in yaw based upon wind direction (or is it assumed that the pilot would compensate for any such changes?).

My question is more about the actual maximum crosswind component. I'm guessing it's merely a "this aeroplane can withstand an X kt crosswind" and then doing elementary trigonometry to determine the crosswind and headwind components of a wind given its speed and direction from the referenced sites. If not, I'm definately interested as to exactly what it is and how pilots can calculate the "effective" (for the lack of a better word) crosswind given a situation.