Some cars have just one power outlet (aka cigarette lighter) to be shared amongst all gadget-using travelers. There are multi-USB adapters that help spread the wealth, but it would be even better if there were two power outlets.
Bestek makes an adapter that splits into two DC power outlets and provides two USB ports for all your charging needs. If you add something like the EleckeyTM or the reVOLT, then you're talking six charges at a time.