Yes, I did think about that but I always thought it might be worth a shot when trying to get my Mac back. It doesn't really have that many important things on it, and never will (everything is on MobileMe iDisk etc), but I just thought I could try to get it back.
I was just thinking about protecting against more 'local' thief's, or thief's who aren't that savy as there are probably still some around.
A 'Find My Mac' from Apple would be good.