Ok, if you have more than one computer, and are not using a KVM, then this is a killer app!
You must check it out.
"Multiplicity is a new program that lets you control multiple computers with a single keyboard and mouse."
I personally have my primary machine, dual-monitor. Then I have a bunch of other machines on a KVM, one of which is on most of the time as my test/media machine.
Now I can move my mouse from one machine to the other, and copy text and images on the clipboard!! The pro version does files as well.