Similar to MouseWizard for the Magic Mouse, jitouch provides a number of enhancements to the multi-touch trackpad (though they claim Magic Mouse support is coming soon). TheAppleBlog has some instructions on setting it up for use with the Magic Mouse. While built for the multi-touch trackpads, this application will work with the new Magic Mouse. It gives 'pinch', 'bloat', and 'tap-clicking' behaviors among others to the new mouse, along with alternative function assignments to the various behaviors. MouseWizard is a very cheap ($2.50) mouse driver that adds a number of options to the Magic Mouse. Despite this, it may work for some people and be fun to check out. It is very much a beta testing project (and should probably be considered in "alpha" development) so while it is a fun experiment, expect it to be buggy. This is a small project aimed to enhance the multitouch experience on Snow Leopard machines, both for the trackpad and Magic Mouse.
There are a couple of third-party utilities and drivers available (some currently in development), which will offer more input options and customizations for Apple's multitouch devices. Likewise, Apple's new Magic Mouse supports a number of gestures, but Apple has limited which can be used in the software. While Apple's trackpads support 2, 3, and 4-finger gestures, the application of these gestures is limited to a few functions. Despite this, there are some limitations to the devices which prevent them from being used at their full potential. Apple has done a great job at implementing multi-touch technology in their input devices, and the new Magic Mouse and MacBook trackpads are hits for most people who've tried them.