Hidden App is a piece of software that can help you locate your mac if it gets lost or stolen. Usually $20 it is available free until January.
From their website:
How it works
When you activate tracking, Hidden will locate your stolen computer anywhere on the planet, collect photos of the thief and screen shots of the computer in use. (We also collect lots of nerdy network information, but we won’t bore you with the details!)
The Hidden team will also help you work with the police when recovering your stolen computer.
Hidden will collect pictures of the thief and their surroundings using the built in iSight camera.
Hidden uses advanced tracking to locate your computer anywhere on the planet to within a few meters!
Hidden will take screen shots of your stolen computer in use so you can see what the thief is doing.