Update 12/23: Who knew that ALL of you would rush over to Hidden and claim your free account? The company has had to close out the free promotion early (as of 12/23), but all registered machines will be valid. [Thanks Chris Pirillo for the heads-up]
Hidden is an app that claims to help you track down and find your Mac -- it runs in the background of your desktop computer, completely invisible, and only starts to send out location information when you actually go to the Hidden website and choose to flip it on. That way, if your Mac is ever stolen, you can log on from any computer and immediately get updates on where your stolen computer is, helping you track it down as quickly as possible. Getting it back is up to you, but just finding a stolen or lost computer is often all you need to do to provide proof that it's yours anyway.
Our own Steve Sande really liked Hidden when we first wrote about it a few months ago, and as a special holiday giveaway, the app is now free for everyone for the rest of the month. That's a great deal -- the software is usually US$20, and most security software of this type is much more expensive, with some even requiring an ongoing subscription. All you have to do is get the app for free and, of course, register on the website (so you can log in to find your computer if needed).
After January 1, the price will return to $20, presumably, so make sure to get the app soon.