If you're right handed, the "correct" way to wear your watch is on your left wrist. If you're left handed, on your right wrist. The same principle applies to a lot of things. Weaponry is the best example, for instance, you wear a sword on your left hip if you're right handed. Makes for a more fluid exit of the weapon (especially with guns. I always floundered with my pistols if I wore it on my right hip). But it also applies to pocket watches, etc.
The reason being has a lot to do with comfort. A watch is a huge pain in the ass when you're trying to write.
But yeah, I wear it on my left wrist. :P