Monitoring Electricity Usage - Real Time

I had been hankering after a real time electricity monitor for a while - these devices basically have a sensor that goes around the electricity cable that feeds into your consumer unit or fuse box (after your meter), with a transmitter attached that sends a signal to a separate display unit.  Some units also allow you to hook them up to a PC so's you can download historical data and draw fancy graphs.

Since it was my birthday recently I decided to spend some money I was given as a present on such a unit.  The cost of these things is typically 40 to 50 pounds for something pretty fully featured.  I was torn between two different devices - the CC 128 made by Current Cost and the Efergy E2.  I finally swung in favour of the CC 128 because I was able to get a slightly cheaper second hand one from an Amazon reseller.  The disadvantage of this unit is that it needs a special data cable which is sold separately for about 8 pounds - and it also doesn't have any software out the box, although a few people have been developing such.
On the plus side it has a much longer history available (once you can connect it to your computer) and it also has multiple channels, so as well as monitoring the power coming into the house, it's possible to monitor individual applicances using the yet to be released IAM (Individual Appliance Module) sockets.

I received the unit today - interestingly it was badged with British Gas - they must be OEM'ing them.  The previous user had used it for 3 days - so the transmitter and receiver were already paired.  A quick read of the brochure showed how to set the time and electricity cost - which was pretty straightforward, although far from intuitive.  I spent the next few minutes playing with switching things on and off - my computer monitor consumes over 100 Watts for example - to see the effect.  Great fun.

My next step was to investigate software.  The CC128 outputs XML - and there are different versions of it depending on which version of the device you have.  My hope of just finding a bit of freeware and downloading it were shortlived.  I did manage to find a suitable generic USB driver which was a start, but my attempts to get any of the other bits of software going have (so far) failed miserably.
Hmmm...fortunately a guy called Dale Lane has done a lot of messing about already with Python scripts and has made their source available - so if I can get the PC talking to the device using some of his code then I may use it as an excuse to learn some Python and do some hacking of my own.  I think the Efergy device would have won out here as it comes packaged with a USB cable and ready to use software.

As an aside, there's pretty good information on the whole country's electricity real time usage on the National Grid Website.