MagicPrefs is more than 5 years old now and is no longer mantained, the functionality it provided was made possible by Api's that are now deprecated and reverse engineered private Apple frameworks. Apple is not likely to replace the deprecated Api's nor provide access to the underlying multitouch technology so that's the end of the line for MagicPrefs and similar software.
TLDR if it doesn't work anymore thats it, if it still works then its just a matter of time until it won't.
MagicPrefs is a free application for OS X which aims to improve the functionality and configuration options of the Apple Magic Mouse, Magic Trackpad and the MacBook glass trackpad.
It features the ability to bind a variable number of finger clicks, taps, swipes, pinch and other gestures to functions like Middle Click, Hold Down Both Mouse Buttons, Spaces, Expose, Dashboard, Recent Applications, Tweet, Read Tweets, Google Reader etc.
Touch Sensitivity implements a single point control for a number of factors impacting the algorithms of the taps, swipes, pinch and other gestures.
Tracking Speed adds the ability to increase the maximum mouse speed by an extra 200%.
Also featured is a real-time display of the fingers touching the surface of the mouse that you can enable to test and monitor the way the mouse sees your input.
Quotes
MagicPrefs is a must download for Magic Mouse owners. This app goes way beyond fixing the tracking speed. Mel Martin, TUAW
MagicPrefs Really Makes Your Magic Mouse Magical. MagicPrefs is a free download, and a must-have for every Magic Mouse user. J.R. Bookwalter, Maclife
Did You Get A Magic Mouse This Holiday? Download MagicPrefs Immediately. MagicPrefs is a perfect example of software making hardware better. MG Siegler, TechCrunch
MagicPrefs Is Like Pixie Dust for the Magic Mouse. If you have a Magic Mouse, you need to download MagicPrefs. Matt Buchanan, Gizmodo
Footprint
MagicPrefs is a application meant to run in the background all the time, it uses less than 1.5% CPU and is optimized for a minimal impact on system performance.
MagicPrefs does not install any kernel extensions not it otherwise have impact on your system while it is not running or disabled, it is not a driver per se, it just monitors the Apple multitouch driver built in OS X to get information about the touches on the mouse, stopping or disabling it totally removes any impact on the system as it stops all monitoring, as for the mouse tracking settings they are changed in real time in the os, to recover them to default values all you have to do is use the Apple mouse preference pane.
Furthermore the core of the application runs separately from the user interface which can be found in a System Preferences prefpane, from which even the menubar icon can be disabled for more transparence.
Design goals
I love the magic mouse and the virtually endless possibilities it presents, the main goal of MagicPrefs is to harness those possibilities.
However endless possibility means complexity, and what i also love is the usability of Apple products because they strive for simplicity.
I feel like a software program for a great Apple device has to strive for the same ideals that produced the device itself so i have went to great lengths to present the complexity MagicPrefs enables in the most simple and visual manner possible.
Some Advice
Take it easy with the gestures, and you will thank yourself for it, jumping into having 5 or 10 new bindings from the start can be extremely confusing, take your time to get comfortable with each new gesture you chose at a time, test it out, let your body get accustomed with the motions involving it.
Ideally a gesture should always trigger when you want it to, and never trigger when you do not, but in practice that is not always the case and the complexity involving this is probably a big reason why apple has not implemented something like this application already.
Plugins
With version 2 MagicPrefs was made modular with optional functionality coming as either free or paid plugins, 3rd party plugins are also allowed and there is public API here.
Plugins tap into the core functionality of MagicPrefs adding additional features, they run under a separate process from MagicPrefs and are automatically kept up to date.
For a list of the plugins and more detailed descriptions see the Plugins page.