Speaking of electric/hybrid cars...

An Austin-based startup called EEStor promised "technologies for replacement of electrochemical batteries," meaning a motorist could plug in a car for five minutes and drive 500 miles roundtrip between Dallas and Houston without gasoline.

http://ap.google.com/article/ALeqM5injP_H-HkCkxCFHZ0ryEBSrvGgWQ

Does using capacitors to power vehicles have a promising future or is it just another perpetual motion machine?

Everything i've read about it before has always been an "in theory if...." type thing.

[I]Does using capacitors to power vehicles have a promising future or is it just another perpetual motion machine?

Ultracapacitors are very, very good at absorbing or dumping a huge amount of power, but they are poor at storing energy - the energy density is maybe a tenth of what lithium-ion provides, and the discharge voltage curve makes much of that difficult to access.

They'll have a place in electric and fuel cell applications (in fact, Toyota's hybrids already use a sizable ultracapacitor in the inverter module), but I really have difficulty seeing the day where they are an outright replacement for chemical storage batteries.