In reply to kwoods:
I've been told that some of the drying agents in some chalks may dry out your hands so perhaps the extra sweating is in some way to compensate? I know mine seem to just excrete all sweat in my body from just my hands when I'm climbing, and the worst thing is when that mixes with the chalk and makes the hold slimy. It is the only time my hands sweat - running, circuits, weight training my hands don't react in quite the same way as they when I climb or boulder. Very, very annoying.