RSI: h'apparently two button mice give you RSI - and h'apparently the one-button Mac mouse is better because your index finger can rest in a much more natural position on the right hand side of the button... so if you've got a two button mouse, configure your computer for a left-handed mouse and then you can put your index finger on the "right" button - much more comfortable.

"The multi-button mouse is a MAJOR cause of RSI/OOS: very dangerous. Waggle your index finger and you can see related muscle movement right up into your shoulder. Holding that finger hovering over the left button sets up a slight but continuous muscle tension that can be very damaging in a remarkably short time if you have to do a lot of mousing. The Mac one (or no) button mouse can be clicked with only minimal movement of the right index finger, allowing that finger to return to a resting position to the right of the mouse." link