I've been using a Dvorak layout for about 7 years now.  I converted for efficiency; at that time I had no wrist or hand problems.  Within the last couple years, intense typing sessions have give me lasting pain in my hands (mostly emanating from my pinky fingers).  The Dvorak layout actually seems to be worse in this regard (pinky strain) than Qwerty, so I've switched to using a Kinesis keyboard, which has helped somewhat.  Though nothing seems to help like backing off of typing for a while, and avoiding long laptop typing sessions.