Well, the privacy issue extends a bit beyond someone intercepting your internet communications by standing underneath a powerline and picking up stray signals.
Once it become common to transmit data over power lines, manufacturers will use such to have appliances signal back to the company. Paq already mentioned the electric company reading your meter by remote control. At first, it will be mundane stuff, such as when the washing machine is due for maintenance. But, I fear it will just be a matter of time before my toaster rats me out for smoking pot!

#$DN
Once it become common to transmit data over power lines, manufacturers will use such to have appliances signal back to the company. Paq already mentioned the electric company reading your meter by remote control. At first, it will be mundane stuff, such as when the washing machine is due for maintenance. But, I fear it will just be a matter of time before my toaster rats me out for smoking pot!
#$DN