Peering into the settings for the magic mouse i have found out what looks like support for 3 finger tap gestures for Dashboard and/or Expose control , namely :
“Dashboard” – three fingers tap
“Exposé All Windows” - three fingers tap to expose all window
“Exposé Application Windows” - three fingers tap to expose app window
“Exposé Desktop” - three fingers tap to expose desktop
These look like the options you would see in a dropdown list from which to select one action associated with a 3finger tap.
Currently you do not have a mouse system preferences option for 3finger , only “One Finger” and “Two Finger” sections are available for now.
Another thing to note is that a 1 finger swipe action is also referenced , and that “Mighty Mouse” still remains as as string reference , if you search for that in system prefs the mouse icon will be highlighted , this could show that apple was really in a hurry on this , sloppy or understaffed , either way here is the system preferences movie for the magic mouse:
Who knows if 3 finger tap functionality was planned but not finished or removed , but it was not entirely built and disabled either , because it can not be enabled as it is.
EDIT : I released a free app to enable adding middle click , expose , dashboard , desktop , spaces , both button holding , etc , the works in my app MagicPrefs
Personally i think a gesture enabled mouse is a great move , and am looking forward to seeing it implemented in more mice , besides the mighty mouse i have been using a Logitech Air mouse which has a touch scroll with momentum which i miss dearly when using the mighty mouse , i am sure the same will be true about gestures.
But for now i want to touch on some issues with the magic mouse , when it was announced i was hoping a old issue with te apple mouses might have been addressed , that is the inability to hold down both buttons , the mouse registers a left click when a user clicks with both the right and the left fingers pressing.
While the swipe functionality alleviates this a bit there are still a number of 3d applications , games , and browsers that need the old “poorman’s swipe” a left swipe being similar to pressing and holding the right button then pressing the left and vice-versa , but this way of clicking can not be entirely replaced by the swipe feature as you can not swipe and drag for example.
What i do hope is that software developers will start to be aware of gesture enabled mice and of mice lacking 2button hold functionality , or even better mice manufacturers start making mice that implement both features , in any event here is a osx application i wrote for the purpose of testing mouse functionality.