Excellent Touchpad and Magic Mouse software
SynergyOSX is a Mac GUI version of Synergy, an open source project aimed at creating an easy-to-use, cross-platform mouse and keyboard sharing system.
If you work between several different machines at once or need to be able to use your keyboard and mouse on more than one computer, SynergyOSX could be very useful. Synergy works between computers independent of the operating system you use so it's ideal for those working between PCs and Macs. It could be especially useful for a video editor who has two different machines for editing footage in the same studio.
Redirecting the mouse and keyboard simply involves moving your mouse off the edge of the screen. When you do this, it automatically transfers power to the other machine. It's also handy for cutting and pasting between different computers because it merges the clipboards into one. Your screensavers will also be synchronized so they start together and your screen lock passwords will also work under one password for both screens.
Setting up Synergy simply requires that you identify an IP address or Synergy Server Name of the computer you'd like to share. If when connected you don't want the mouse to cross screens at any point, you can just activate the scroll lock. When you require screen sharing again, just switch it off again.
Overall though Synergy is a useful application for those who work on dual screens or different machines, and don't want the confusion and clutter of another keyboard and mouse.