Chris S. was telling me about Multiplicity yesterday, and it seems like a pretty cool program. Apparently, it's a robust software version of the good old KVM.* The difference though, is that Multiplicity only shares the keyboard and mouse; every computer must have its own monitor.
Basically, it allows you to share one keyboard and mouse among several computers. It doesn't do this in the traditional KVM switcher model, but rather over your wireless network. I believe that each computer listens on a certain port for it.
The software claims to be able to perform text copy/pastes between computers and even allow for file transfer - you can right-click and copy a file or folder on one machine and right-click and paste on another.
Overall, this seems pretty nice if you run multiple computers on the same desk, but I would make sure you're up to date on your network security before running this. The first thought that came to mind when Chris told me about this was: so, since you're using the wireless network, aren't you like broadcasting all of your keystrokes in a 150ft radius?
* A KVM is a hardware device that allows you to use one keyboard, monitor and mouse for multiple machines. Usually, there is a keyboard shortcut or a physical button on the KVM that allows you to switch between machines.