I've been thinking lately;
* A lot of luxury cars use cards instead of keys nowadays to start eh?
*A lot of people have an iPod in their car eh?

It should not be to hard to combine those two, so that when you put your card in your car to start it, it is also a usb mp3 player, so that you always have your own music collection with you when you drive...
Might that be an idea? Trademark etc to me
-Joost-