Capacitors are be the nature of the definition "rechargable" and if you have a capacitor that holds a large enough charge for a long enough time you have something that is pretty much a battery (although they usually call them "supercaps"). The trouble with the caps in most computers is they are cheap electrolytic caps and they break down over a period of time. These caps look like little tin cans on the logic and power sections of the computer and when they start to break down they kind of swell and pop on the top and start to leak electrolytic fluid. We've had a number of Lenovo/IBM PC's break down in less than 5 years and I know there were HP's and Dell's that had the same problem. We had small Dell unit's in our school lunchrooms that were left on 24/7 and they sometimes show bad caps in a 6 month period. There isn't enough information about the long term lifespan and such of these new caps but it seems like the technology, and the stability of the nanotubes, are "very" promising!
