I've written a Raspberry Pi-based electricity usage monitor: http://c.cam108.me/energy
The hardware is simple: A USB hub back-powering the Pi with a Belkin WiFi dongle in one of the ports, and a single phototransistor on the GPIO port pointed at the flashing LED on my meter.
There are more graphs here: http://c.cam108.me/energy?more?daysago=14
showing time-of-day average and daily totals.
I will write up the details if anyone is interested in the details.