the system we developed used an asic to do all the signal processing for the spread spectrum tx/rx we found that data rates of 2400bits per second could be maintained over distances of 2-3 miles,with frequency hopping at 10 times per minute as long as there werent many joints in the cable because the jointing technique used is terrible for rf signals.
The main problems dont show up until you try to transmit the signals outside a single house or you cross the boundary where you change to a different substation because then you have the problems of getting the signals onto different supply phases.
Motors are a pain in the arse where this kind of think is concerned as are switch mode power supplies we found that you couldnt get reliable comms when there was a heavy use of TV's such as in the evenings.
I think philips are doing a lot of X10 devices for use in single houses