Watched a youtube video
http://www.youtube.com/watch?v=gsYWnOnPIxQ
on this device. If it is the one you are thinking of, I don't think the power companies are going to be too concerned. The circuit will convert RF into DC, but not very efficiently. I reckon they must have had the antenna wire hooked up to a signal generator to get enough oomph to start a 3v phone battery charging. Either that or had the AE running for about a mile underneath a HV power line! If you could design an antenna to suck in all frequencies in the RF spectrum, you might be able to get useable voltages out of it, but without that, I don't think I'll be converting the house over!
Ken