Once I got a library book written by an MD about repetition stress injuries. He specifically mentioned using a guitar pick as a cause of damage to the hand. I think it's fine to use a pick, but don't use it all the time, and don't use it for hours.

What, and the FRETTING part doesn't cause repetitive stress injuries? It's my left hand/wrist that gives me more trouble than my right.

What exactly did he say about it: Gripping the pick too tightly? The hand motion associated with flatpicking? Poor positioning? Something else? I would think that fingerpicking, which is also repetitive motion, would have the potential to cause problems, as well.

From what I've heard, playing music, period, can be hard on your hands. It seems to be the harpists and pianists I know that complain the most, but others have admitted to it.