Interesting design competition - and here are the top entries and their votes, with posts pro and con about them:
Apparently this was discussed in Dwell Magazine as well, but I don't have an immediate link.
This is one entry, for example -
(quoting the description from the greener gadgets site) ---
Power-Hog is a power consumption metering piggy bank designed to sensitize kids to energy cost associated with running electronics devices. Plug the tail into the outlet and the device into the snout; feed a coin to meter 30 minutes of use.
It's designed to capture the interest of parents and kids alike and serve the wider environmental cause. Power-Hog visually and symbolically associates power conservation with savings by using the iconic piggy bank as a visual reference. Kids can use their allowance to turn on the TV or video game by feeding the Power-Hog with loose change. The Power-Hog meters consumption and blinks red when time is running out. It also helps parents meter the amount of time spent watching the tube. (end of clip)