I'd go for correctly implemented encryption. No need to pull the kill switch
Agree with scancode & f0dder.
Encryption's far better than deletion for security. Encryption can be done in one pass. t would take multiple read/writes to securely delete something such that it would be difficult to recover. And the huge amount of disk activity would be enough to tip somebody off that something unusual was going on. Anybody with a modicum of technical knowledge would put two and two together in about a minute and just kill power to the box. Encryption could be set to silently run in the background and do its work without unusual disk activity.
There was a program called Dead Man's Switch
that did something similar except it activated automatically if you didn't
contact it. Basically, it would initiate a number of actions (i.e. send out e-mails, encrypt files, etc.) if it didn't hear from you after a predefined interval. It was originally written around the time of Win2K. I don't believe it's being maintained any more (the author was probably worried about liability if it ever malfunctioned) but it is still available for download if you google it. Use with caution since it's dependent on the system time reported in Windows. If you (or some piece of malware) monkeys with your date or time settings, it can accidentally be triggered.
The real weakness with this type of software, however, is that it only stops casual thieves and morons. That's because it relies on the stolen device to be running in order for it to work, A real data thief will just pull the drive out of the machine and mount it on another PC so that none of the executables will be active. Then he can browse what's on it at leisure. Once he grabs what he wants, he'll just wipe it with something like DBan, install a Linux distro, and head on over to a flea market (preferably out of state) to dump it.
In order for what you're proposing to be usably effective, it would have to be hardware-based, controlled by the BIOS, and use to a serialized hard drive keyed to only work with a specific motherboard. That puts it in OEM territory. I believe there are already some laptops that implement full disk encryption using such a system.
(Hmmm...finally starting to get a little worried about that 8GB JPG "Art Collection" you've got, eh?