Good thread John,
When I was with the PoCo here, I used to do "power analysis" work, which is to a degree what you have in mind.
If you want to do this sort of thing with any authenticity (not to be-little the Kill-A Watt at all), you need to get a decent data logger that will interface with a laptop computer and give you real information.
The data logger I use will connect to any circuit at it's origin at the panel, it gives voltage and current at any given time during it's connection.
I have to also agree with the con-census here, people doing power analysis work are going to be in bigger demand over the next decade or so, this will not be a loss leader, especially if you get into some of the commercial buildings and factories that seem to waste a lot of power un-necessarily, your work will be paid for by lower power accounts, in a time where energy costs are going through the roof.
Doing this sort of thing at a residential level would however IMO be a waste of your time and money, think free estimate.
