I am a small ISP here in Washington state.
I am one of the 1st ISP's in the nation to be involved in broadband over power lines. This is because we have a local public utility company here who is involved in running fiber optic cable to every home in Chelan county here. As a side venture they are testing BPL as we call it. My company setup the 2nd connection in a small local town that had no cable or dsl.
We are using it as a stopgap measure until we get the fiber to the homes who want broadband. We so far have had no issues with interference with local ham radio.
It is capable of about 400k up and down.
I don't know the exact distance this works but the PUD tells me it is only viable for very short distance. With this limitation most of the areas that will be served will be areas where such things as dsl is already available.
To cover long ranges such as rural areas you would need to install repeaters in the power lines. This is where things get real gray as this has not been shown to work at all with local testing in our county.
As with anything with a lot more money thrown at it this can possibly be overcome. Maybe with google type money they will figure out how to wire whole counties etc.
If this limitation was overcome this could be used to cover large areas and then it would rock as large rural areas are without broadband and because of population density and thus high cost will probably remain out of the broadband loop for a long time.