No one is doing that yet. However there are two possibilities I know of.
1) Echelon is selling power meters with Lonworks powerline communications in them, but only in Italy so far.
2) The other possibility would be to hack this guy http://www.powercostmonitor.com/
and use its radio link to talk back to the core. Then work out some software to analyze the power usage and relate it to time and controlled devices. If anyone is up to the software side I'll volunteer to get the attention and cooperation of the vendor if possible.