I am able to map out three and four finger gestures on the Apple MagicMouse to trigger Expose (3 finger tap) and spaces (4 finger swipe up and down) using a program called BetterTouchTool. Because of the width of the magic mouse you can see 4 finger swipes are kind of weak, you have to have your fingers on the surface just right for it to register although I am becoming more successful with practice.

Also, using synergy to share a single mouse/keyboard with an additional monitor attached to a PC. (less info)