Five years after the cool kids first started jumping on the bandwagon, I've got myself a CurrentCost CC128 (Southern Electric send them to some customers for free, it seems - e.g. my granddad who didn't want it).
So, with the addition of an eight quid data cable and the Linux box running in my lounge, may I present my electricity usage graphs. Bear in mind that these are (at the time of writing) for a five-bedroom house in central Oxford.
The parser for the XML output of the device I'm using is this one - just swap "COM20" for "/dev/ttyUSB0" in their testrun script and fix it to ignore empty lines read from the serial port, and you're in business. I then hackdapted this RRDTool tutorial to plot the graphs.