I have a Contour rather than a GoPro, but the idea is the same. I mount mine on my helmet sometimes, plus I have a frankenpole. The head-mount is ideal for filming someone else while you're following them down the slope, because the viewpoint follows where you're looking. One problem with snowboarders though is that your head isn't necessarily totally vertical. With the Contour you can rotate the lens to compensate. Not sure what you'd do with the GoPro.
The Pole mount allows you to see what you're doing, either from the front or the back. But it throws you off a bit until you get used to it, and you can't really do things like spins off jumps.
Ideally the best place for a cam if you want to record yourself, is on a pole in the hands of a friend or on the helmet of a friend.