[jonty]

Agreed, switching to a trackball is the only thing that solved my wrist pain issues.

Its worth spending money on a decent one, and I'd avoid Logitech units if you have a choice. The main things to look for are ball size and extra buttons - yes, you can get two-button trackballs with no scrolling ability or third button.

I highly recommend the Kensington Slimblade, which has a massive ball and lovely twist-to-scroll mechanism. Ignore the reviews saying the software is terrible on OSX, all the problems have been fixed.

http://www.amazon.co.uk/Kensington-K72327US-SlimBlade-Trackb...

One slight oddity is the hardware "clicker". Twist-to-scroll feedback is achieved by a tiny piezo speaker inside the unit that clicks whenever you scroll. Its worth spending ten minutes with a screwdriver and soldering iron removing it if you want to keep your office mates sane.