Although there have been previous tips published about speeding up your mouse (one, two), neither solution was perfect. The first tip required replacing an Apple kernel extension; the second didn't change the settings in real time and was often reset arbitrarily.
Ben Hines has just released MouseZoom 2.0, a freeware solution that handles both issues. This system preferences panel installs and removes easily, and (as of version 2.0) the changes made are reflected immediately in the speed of the mouse tracking.
MouseZoom 2.0 is a more flexible solution than replacing the stock Apple mouse driver, as it is very easy to revert to your original setup - just remove the preference pane if you don't want to use it. Thanks to 'greggomer' for telling me about the updated version.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020111102142108