Enerjar and Other Winners of the Greener Gadgets Design Competition
The winners of the Greener Gadgets Design Competition have been posted on the web, including the Grand Prize winning Enerjar, the "do-it-yourself power meter." There are several smart, interesting designs, but the Enerjar really does look great, with plans and software to be distributed freely on the web. (Now I just need somebody to build a one-click parts pack for order so I can build one myself without having to source all the individual items. Hint.)
Winners Page [Core77.com]
Update 03/03/08: The designers of the Enerjar have now put build instructions online.

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My guess is that this is a device given by miserly parentals to a subteen to make them feel guilty for leaving the lights on. "See Bobby, your Game Boy Advance is costing us 53 cents a month!"
You could use it to prove to drunken friends that the wall warts do really use electricity when not being engaged.
I'm sure it is just one of many new anally- retentive products soon competing for our attention.