I have the Performance Mouse MX on my work computer, and the Magic Mouse on my home computer. The PMMX has great ergonomics, and a bit smoother action on a desktop, and I love the free-wheeling scroll wheel, BUT, once you actually get used to the Magic Mouse, the scrolling with momentum (only on SL) and customization available with gestures (with BetterTouchTool) beats the PMMX hands down. Once you get used to the ergonomics of the MM, it's fine too. You just have to get used to not resting your palm on the mouse, I grip it on the sides with my thumb, ring/pinky fingers.