I started using the mouse regularly when Mac first came out (I used mouse before but not regularly) and my fingers were fine for 16 years.  The trouble started when I started using mouses with scroller wheel which is most conveniently accessed using my forefinger, the same finger used for mouse clicks.  After two years of mousewheeling, the tip of my poor forefinger is sore, peeled, and hardening.

So I spent a few minute trying to figure out why mouse wheeling hurts where clicking doesn't.  The answer is that, while clicking is done using the flat area of your fingertip, wheeling uses whole length of the fingertip.  Most common mousewheeling action is scroll down (to read), an action that starts with the flat part of fingertip touching the wheel and ends at the area near the fingernail.  That area is almost never used — poking is not a common activity — so its gets sore really fast.  After two years of it, I have to give my fingertip a 1 minute every 15 minutes or so.

This is why HCI is hard.  A cool new feature could mean either whole lot of evil fingers pointing at you later or our forefinger will evolve to rival the thumb in the future.