My guess is power correction too possiblty caps. Residences are "poor" when it comes to power factor. Friges, freezers, air conditioners, any motor loads like hand held appliances have "poor" PF. I would imagine that is one of the reasons why residential kW rates are higher. Large commercial users pay for the PF issues.
Except that these are only a very small %, and mostly intermittant- you're not going to save any money pf correcting a garbage disposal or garage door opener for the few seconds a day they're running. The vast majority is simply resistive or of a nonlinear sort that wouldn't be helped by a pf cap- lighting, water heater, stove, clothes dryer, electronics, etc. The only load that would really be helped by this is the AC compressor. And with natural seasonal variations, you're never going to be able to prove anything without a GIANT study.
Residential pf is typically .92-.96. Here's a small poco study actually looking at the effectiveness of residential power factor correction caps:http://www.kvarhydrosave.com/sites/kvar/gfx/Residential_Power_Factor_Porrection_Project_2005.pdf
Redsy: did you point out to your friend that electic bills are all an estimate based on past useage, and that his "$10 savings" is actually reflecting the month's usage BEFORE he got the pf correction, and more likely just because the weather is more temperate right now than any of the snake oil he wasted his money on?