Over on his blog "K-roy" has completed a writeup discussing how he is using an RTL-SDR dongle to monitor and graph the power usage of his home. After seeing multiple ads for the Sense home power usage monitor, K-roy decided to roll his own similar device instead.
Many homes in the US and elsewhere no longer require meter reader personnel to come onto the property to read a physical meter at the back of the house. Instead the meter transmits wireless data in the 900 MHz ISM band about electricity usage, and all the meter reader has to do is turn up outside the house and take a reading from the street.
These electricity usage signals are unencrypted and can easily be decoded and displayed with an RTL-SDR and a ready to use program called rtl_amr. The signals even travel quite far, and there have been reports of receiving neighbours signals up to 600m away. K-roy took his RTL-SDR and rtl_amr and wrote on top of it a program that creates a JSON output of the data for easy processing, a PHP, SQLite3 and JQuery based database system for storing the data, and an HTML5 based page for graphing and displaying the data.
If you are interested, there is also a discussion about K-roy's work over on Reddit.