When you think of security for the Mac, you're usually talking about firewalls, encryption products, and (most controversially) antivirus apps. But there are some much more brass-tacks security products on the Macworld Expo show-floor that have nothing to do with hackers or malware.
Orbicule's Undercover, Gadgettrak's MacTrak, and Absolute Software's LoJack for Laptops each in their own way make it possible for you to track and (it's hoped) recover a stolen Mac.
The basic idea is the same for all three: You install some client software on your Mac and register it with the vendor. If your laptop is stolen, that software can (depending on the app) transmit its IP address to the authorities (who can use that network ID to find the laptop's physical location), locate it via Wi-Fi triangulation, or even take a picture of the perp using the laptop's built-in camera.
To keep your laptop from being stolen in the first place, you could lock it up. Kensington is most famous for its laptop locks; Mac laptops have long had special receptacles for such locks built-in. But the MacBook Air is too thin for those receptacles. At least two vendors at Macworld Expo–i2 Electronics and Noble Enterprises–were touting some clever solutions to that problem.
In i2's case, that means a bracket that slips over the MacBook Air's screen; attach a cable and lock to the bracket, and your laptop can't be snatched off your desk. Noble's solution is a thin skin that attaches to the bottom of the MBA, with two thin feet on the bottom that provide stability and a place to attach a lock.
Not the sexiest products at the show, but some of the most practical.