Awhile ago, I ditched my Magic Mouse for my old wireless mouse, and for several reasons:
1) I kept running out of batteries (It does not last for 4 months...)
2) I was starting to develop RSI from the ridiculously bad tracking of my huge 24 inch screen (even at maximum track sensitivity it
would take my whole mouse pad to track to the edges of my screen)
3) I was bored with the swipe gestures that Apple had given to the Magic Mouse by default.
This nifty little add-on is what I was waiting for Apple to eventually with new gestures for the Magic Mouse, but instead has been done for free by a third party. It addressed issues 2 and 3 with even higher tracking speeds (bye bye RSI) and a whole truck-load of new swipe features!
I've been playing around with it all night, and to summarise, it basically makes your Magic Mouse almost on par with the Macbook Trackpads. This is saying a lot because in addition to scrolling and going back and forth (boring) I can now:
>Middle click (to open new tabs!)
>Expose with 2 finger swipe down
>Show desktop with 2 finger swipe up
>Switch spaces with 3 finger swipe up
>Bring up the dashboard with 3 finger swipe down
>Bring up a nifty little magicmenu when triple clicking (easy access to copy/paste without touching the keyboard)
That's not even half of the things you can add, although half of the gestures there are probably not ergonomical or convenient to do unless you have epic spider hands.
At any rate, if you have a Magic Mouse (or is considering getting one) then MagicPrefs is a must have!
Check it out here