AC Power Usage Telemetry via Radio

I've been wanting a way to monitor when different things around the house are on (sump pump, furnace, etc.). I've been thinking about a little box you plug into an outlet and then plug the device into the box. Inside the box is a radio transmitter that reports when things are in use. Then I found this: http://www.ladyada.net/make/wattcher/. Awesome! Just about exactly what I was thinking about.