Powerline Networking

While wireless networking seems to be getting all the headlines and buzz, another networking method is to use your existing powerline. There are a couple of associations promoting this, with two to three dozen manufacturers and a few chip designers supporting the technology. The concept being– why create something new when you can use what already exists in your home. I'll admit I don't know all the intricate details behind this technology but the first thing I can see as a negative is all the extra external devices (i.e. wall warts) you are adding to your electrical outlets. It just doesn't seem very green to tax the power grid even more. What I would like to know is how does this effect your electrical bill?