Customize the Magic Mouse: middle-click, taps, pinch, etc. (apple.com)

This was the clincher for me to buy a Magic Mouse. Extreme customization options. 2,3, and 4 finger clicks. Taps (including a "stem tap" on the apple logo). 2 and 3-finger swipes in all four directions. 2 and 3 finger pinches. And it's free.