Ergonomics of the Trackpad

I use my Macbook Pro a lot of the time (usually more than 8 hours a day, if Time Track is to be believed), and its multitouch trackpad is probably my favourite feature. I use it all the time, have all the gestures committed to muscle memory, and have even created some gestures of my own thanks to BetterTouchTool.

But still I sometimes worry what that does to my hand, with regards to repetative strain injury, etc. After a long-ish period of use, my scrolling fingers do feel a little stiff. And whilst it's not a major problem yet, I do want to get into good habits.

What do you recommend to ensure my hands last me into old age? I am left-handed, but I use my right hand primarily, so perhaps I could learn to switch to my left hand for short periods. Any tips for doing this?

I am tempted to buy a Magic Mouse, and use it some of the time when I am at home. The one thing putting me off is that a lot of people have said it's not very comfortable. I know it doesn't do all the gestures, but I can use BetterTouchTool to fill in the gaps, so that's less of an issue. If anyone here owns a Magic Mouse, could you please tell me about your experience with it. Is it too small for your hand? (My hands are about average size)

There was a rumour back in August of a Magic Mouse refresh (when Apple discontinued the part number). I could certainly hold out a few months longer if they were going to release a better one, especially if it was ergonomically improved. What are the chances of this happening?