Have you been hiding under a rock? This activity has been hotly debated for a couple of years at least.
The fact is that power lines are not designed to conduct high frequency signals, so they work more as antennas than as conductors. The result of broadband over power lines (BPL) is to create a high level of pollution of the high frequency radio spectrum. Radio amateurs have made the most noise about this, since they stand to lose the use of the HF spectrum; but shortwave radio listeners and business and government users of the spectrum are also complaining. The FCC seems to be taking a position that it is OK to foster the growth of a new business rather than to protect the existing radio users. Field trials have been done here and there and have shown that the radio interference potential of this activity is serious. There is also the possibility that nearby radio transmitters will disrupt operation of the BPL system.
It's not something you want to invest your savings in.
jhhaynes at earthlink dot net