I've been saying for a while now that Apple needed to do something to bring multi-touch to its desktop lineup. Well, now they have. I bought a couple of Magic Mice - one for the mac mini in the living room and one for Scarlet's desktop machine. It works more or less exactly like it's depicted on its website. The scrolling with momentum is particularly welcome. It's a great way to scroll through big web pages and documents quickly. I actually hope that they add that feature to the multitouch laptops as well.
The two finger swipe gesture works with Safari as a "back" and "forward" nav action. I didn't think that would be useful at first, but I've actually found myself using it a few times.
The one gesture that's missing is a pinch gesture to zoom in and out (the pinch in Safari makes the text size larger or smaller). A close second best is the control-scroll gesture to magnify the screen. That works really well for the mac mini in the living room as a nice compromise - 720p is too low in resolution, but 1080p makes the fonts generally too small.
If I have one complaint, it's the packaging. They used tape to secure the mouse inside its box, but that tape doesn't come cleanly off - it leaves a nasty, sticky residue behind, and that residue was keeping the mouse from moving smoothly on a mouse pad. I had to break out the Goo Gone to get rid of it.