My major concern is that there's talk about using supercapacitors in portable devices, and notably in cars. The concern being that capacitors are specifically designed to discharge quickly, to the point that a shorted (IE purposefully connecting two terminals) capacitor quickly explodes.

The concern being that should we start filling the floors of hybrid vehicles with these, that we are essentially deploying fast moving bombs on our streets, roads and highways, and all we're going to rely on is faith that someone isn't going to put a switched connection between two terminals and wait till they're parked outside a police station, abortion clinic or elementary school and just flip the switch.