I use an arduino for doing the same, the CT route was my first bit I did. I found a toroidal current transformer on Ebay and used that for the interface. The problem with current transformers and using the arduino as an AC voltmeter is that what it measures is Apparent Power (Volts * Amps or VA) What you get billed for is Real or True power (Watts) . The difference between the two is whats called the power factor. Cheap computer power supplies in particular tend to have terrible power factors, so there is a wide discrepancy between the two. My next step was a reflective object sensor (an IR and photo transistor in a common housing) to measure how long the aluminium disk takes to rotate on the meter. I then plot them on the same graph. I've added quite a lot of other stuff and the result can be viewed here :
http://pluggy.is-a-geek.com/index.html
I haven't published my methods yest as its forever evolving. The last graph is a digital plot of the ADC against time and shows the waveform coming out of the current transformer. The difference between it and a sine wave is effectively a measure of the power factor. When I turn on an heavy power device with a good power factor (Electric Kettle - a resistor with little or no reactive element) the graph smooths up into a pretty convincing sine wave. Most of the time when its running my computer and TV and stuff, its a spikey mess. The gas graph is the same technology as the electric meter - watching a reflective bit on the last reel of the meter.Not much happening in summer as I don't burn much gas. The temperatures are 'Dallas' one wire digital thermometers. and the light levels are LDRs in a voltage divider circuit. One of these days I'll do a write up and take some pictures.......