I have read and heard contradicting personal experiences on how much stress on the hand, wrist and arm Apple's Magic Trackpad put compared to a traditional mouse.
E.g.
http://softwareprototyping.net/is-your-apple-magic-trackpad-giving-you-rsi/:
I am starting to suffer from pain in my right hand which I am wondering might be due to the use of the Magic Trackpad.
http://erikrunyon.com/2011/01/rsi-and-the-magic-trackpad/ :
Back to the question of RSI. After three months of use, I’ve noticed a significant decrease in pain
Does Apple’s Magic Trackpad put more stress on the hand, wrist and arm than a traditional mouse?