Trackerballs not always the answer
I had mouse-and-keyboard related injury in my wrist by around age 28, so I switched to a Logitech thumb trackerball. Bliss! It meant I didn't have to move my hand at all (great for flights), was more precise, and the inertia of the ball meant you could spin it to move around the screen....
...until I developed thumb RSI earlier this year (age 34 - and I use my Blackberry a lot too). Yep, I said "it wouldn't happen to me", too. Vitamins, Cod Liver oil, jogging, gym - all the usual keep-your-body-healthy stuff. I thought I'd spend the rest of my life with 'special' aids for typing, but luckily my hand's recovered a fair bit and I can work normally, as long as I don't overdo it.
So now I use the glidepoint on my laptop. A lot slower. Who knows, in another couple of years, I might get ring-finger RSI, and have to move to another option. So this mouse is of particular interest to me - I might be able to expense it, too.
Don't scoff kids - listen to that Health'n'Safety blurb, pay the money, and save your wrist for more important things*.
* Like Badminton.