Haha. I was going to respond to the DoD card thing as saying, well, people could just gain acess to your card. but you're right, people could also gain acess to your fingers.
High-end professional biometric systems are very sophisticated, sufficiently so that they can detect whether there is warm blood pumping in a natural way through the particular organ in question. You may still find yourself incapacitated in some way so as to supply your body part, but these sorts of systems are usually installed in facilities where security cameras would make it difficult to hide that something is amiss.
The sorts of biometric systems most people are ever likely to encounter, on the other hand, range from "screen door" to outright joke. Vendors of such systems make claims that are demonstrably false.
The sort of fingerprint scanner you would find on your laptop could be successfully thwarted by dusting a convenient surface for your fingerprints (like, say, the keyboard of your stolen laptop) and using the results to produce a sufficiently convincing prosthetic to fool the scanner.
But seriously, that seems a little far fetched. I'm talking about preventing casual theft. Someone grabbing your iPod and running, snagging your laptop when you're not looking. If it became useless immediately afterwards, don't you think it'd work? Not every thief will know how to hack something. It seems easy to implement.
A casual thief is not the threat model for any access control system. The thief does not care about the contents of your laptop. He is willing to look online to find the customer support directions to reset the device to its factory state, wiping your data in the process. If he cannot find it, or is too dumb to look, he will simply trash your device or sell it to some other sucker. Your device is still gone, and the biometric device has not served as a deterrent.
Thwarting the attacker who cares about what's on your laptop is why you want an access control mechanism. There are certainly casual attackers who would be thwarted by a fingerprint scanner (your little brother, say), but a good long hard-to-guess password will thwart your little brother
and many more sophisticated attackers. Don't assume the more futuristic-seeming solution is the more secure one. The current state of consumer-available biometrics devices should not be considered serious security.
