The Tweet-a-Watt project was good - in fact good enough to win a competition - but there are a few obvious flaws in the first iteration of the design. Not least is the requirement to have a computer turned on to receive power-use stats and tweet about them; now Adafruit Industries are back with their solution, a hacked $40 ASUS router with XBee wireless capabilities.
Video overview after the cut
Basically the router - which normally just handles WiFi - is reflashed with OpenWRT, and an XBee wireless module is soldered onto the serial port header on the router's board. Then, rather than needing a full PC on to do the Twittering, the router itself can do it while also sharing out your home broadband connection.
Full instructions to reflash the router are available here, as part of MightyOhm's WiFi radio tutorial. The Tweet-a-Watt kit is available now, for $90, but you'll need to supply your own router and Kill-a-Watt power meter.