Avoiding carpal tunnel is much more of a concern now than whether the input device is good for gaming. A friend of mine got hit by this recently, and ended up buying a RollerMouse Pro 2. Seems like a pretty device (and insanely expensive!) nifty, although it takes a bit getting used to - different sensitivity than using a mouse, and you don't have your usual Mouse Muscle Memory. Bonus point for using optical sensors instead of being mechanical, probably also part of the reason why it's not exactly cheap.
-f0dder
Yes, that's what I've got, though it wasn't for carpel tunnel problems; mine was shoulder extension: having the mouse too far away from directly in front of my shoulder.
I've got one at home and work bought me one for the office as well (in fact, two other people at work now have them too).
Man o man, those Contour products look so nice! I have the Logitech Marble Mouse but I use it sparingly. Every time I get going with it the scrolling ends up throwing me back to my Logitech G9. I think that scrolling - or lack of it, actually - has always been my bane with track balls.
But I love the looks of the Contour Roller Mouse and the Kinesis Freestyle Keyboard made to fit it!
-J-Mac
That's been
my exact set up for over 18 months now: it's saved my shoulder
For the RollerMouse, the distance you have to move your hands is much shorter - I haven't used it enough to know whether you end up accidentally moving the mouse pointer around with your wrists, though 
-f0dder
In fact I keep my fingers on the keyboard and move the mouse with my thumbs (for simple things). You can click with the roller bit too, so simple button clicks are possible too. More complex mouse operations need a little more control than I have in my thumbs so I can use either hand...
It does need a little getting used to, but I don't accidentally move the mouse any more. Getting the relative heights right is important though: the contour comes with "lifters" to help align the height with the keyboard.