A quick take on what designers can do with a few extra Farads.
An Electronic Power Bar
Ultracapacitors, from postage-stamp-size units of a few Farads to multithousand-Farad cylinders the size of a large soda bottle, achieved affordable price points only a few years ago. Since then, they've been penetrating a range of markets in applications where batteries aren't enough. They're used wherever a quick burst of energy is needed. They also store surplus energy.
Ultracaps on Circuit Boards
Some automatic utility-meter readers (AMRs) are used in clusters monitored by a basestation on a utility pole. While they're recording, they operate on a trickle of current. But when they have to burst out a transmission, they require bursts of power. In AMRs, small ultracaps rated at a few Farads are trickle-charged during the AMR's data-collection phase of operation, storing energy that is used up in a few seconds during transmit. If mains power is ever lost, there is generally enough energy in the ultracap for a power-out alarm message from the meter to the basestation.
In an outdoor application like this, ultracaps have the advantage of a much larger operating temperature range (-40°C to 70°C) than chemical batteries. They also have a 15- to 20-year useful life through hundreds of thousands of cycles of charge and discharge without requiring any maintenance. (And the diagnostic for checking the health of an ultracap is simply a matter of monitoring discharge time through a known resistance value.)
Small ultracaps perform a similar duty in some digital cameras. When a photo is being taken, the camera requires several bursts of power for zooming the lens, writing to memory, and flash. In cameras, the ultracaps are paralleled with the lithium battery to extend the life of the battery significantly.
Future applications will find ultracaps tied together with fuel cells to provide instant power while the chemical process in the cell ramps up its output voltage.