Cool, it's always good to see you considering more features Mastero. You the man!
BTW, if you use the ignition/ACC signal for the switched +12v lead then wont this circuit send a pulse every time the key is switch from off to on (even if the computer is already on)? Suppose you have a large shutdown delay to keep your pc running during stops at a gas station. When jump back in and restart your car, your computer is going to receive a pulse and start to shut down, isn't it?