WSJ reported on Thursday about a service offered by Absolute Software Corp. under which you download tracking software to your laptop, which then sends a signal to the service's monitoring center every time it logs onto the internet. If you report your machine missing, the service will be able to trace the computer by its Internet protocol address. "The company then works with law-enforcement agencies to recover the laptop by locating the network it has logged on to - say, a local coffee shop." The article mentions two other such services, Cyberangel Security Solutions and Brigadoon Security Group.
I haven't read these sites with any care, but it seems to me that the thing to do is for the service to send a virus to the computer, having preset a sort of portal so that it gets by the firewall or general virus security. (I am assuming that everything would be backed up, so you really can survive without the machine.) Or maybe the signal would simply lock the Laptop down, if there was any chance of actually retrieving the machine.
And I would have it connected to a little mp3 program that would scream, "Help, Thief! Help, Thief, Call the Police!!!"