This article in today's Fresno Bee describes how PG&E is giving "energy orbs" to major users. The orbs change color color based on energy demand (i.e., shortages).
I talk about ambient interfaces like the energy orb when I teach HCI (CSci 291T at Fresno State and ICS 664 at the University of Hawaii). My favorite is the ambient pinwheel: the more unread email messages, the fast the pinwheel spins. If you are running OS X you can get a similar dashboard widget that represents your unread emails by the number of flowers in your virtual vase.
The first commercial ambient interfaces I remember seeing were from Ambient Devices. You can see a fuzzy picture and read a paragraph about the ambient pinwheel at this archived web page.