Our love affair with carbon nanotubes continues unabated; the latest reason is research at UC Davis demonstrating a process for building high power supercapacitors using carbon nanotubes. Supercapacitors deliver a fast, powerful jolt of electricity; hybrid and fuel cell cars require high-power capacitors in order to start the engine, something typically done multiple times throughout a trip. Remember that hybrids are designed to cut the engine any time the vehicle stops, then restart very quickly once the brake is released. That takes power.
What makes the carbon nanotube-based supercapacitors interesting is that they have a power density of 30 kilowatts per kilogram, compared to 4 kilowatts/kilogram for commercially-available capacitors (and 20 kW/kg for experimental versions of traditional designs).