BPL involves sending data in the form of electrical signals over power lines designed and optimized for 60 kHz signals. Unfortunately, power lines weren't built to handle BPL, which operates at 2 to 80 MHz. Power lines are unshielded, and they make the world's greatest antennas! So what? The result is "spillage" of the signal all over the radio spectrum in the 2 to 80 MHz band. You can see what uses these channels on a frequency allocation chart. An amateur radio-specific chart is here. Spilling noise all over this frequency range eliminates the ability of amateur radio operators to respond to crises like the northeast blackout and 9/11. (This Slashdot thread on hams helping during the blackout shows the public needs to be educated on the sorts of services amateurs provide during emergenices.) More than just amateur radio is affected, so I expect the military and other organizations to complain as well.
You can submit a comment by visiting the FCC Electronic Comment Filing System and selecting "Broadband Over Power Line (BPL) - Docket 03-104." (For some reason the NOI claims number "03-100" while the BPL issue now uses 03-104.) Here's what I submitted:
"I am writing to oppose deployment of Broadband over Power Line (BPL). I am an amateur radio operator. It is wrong to allocate 78 MHz of spectrum (from 2 to 80 MHz) to BPL, when amateurs are already licensed to use large portions of this spectrum. Amateurs provide critical service during emergencies, such as the power blackout in the northeast. Without access to the frequenices planned for allocation to BPL, amateurs would not have been able to communicate with each other at the distances needed to coordinate emergency services. I concur with the documents submitted by the ARRL and I request the FCC consider the ARRL's submission."
For more information, Slashdot carried a recent thread with many thoughtful contributions by amateur radio operators. Amateur radio operators might prefer QRZ's thread and should also read the most recent ARRL story. A video (.mpg) shows what happens to the amateur bands when near BPL-enabled power lines. Wired gave its take, with a quote of support by the FCC chairman. (Here's hoping Congress will step in again if Powell gets his way.)
During emergencies amateur radio operators work within two organizations: ARES and RACES. The Amateur Radio Emergency Service (ARES) consists of licensed amateurs who have voluntarily registered their qualifications and equipment for communications duty in the public service when disaster strikes. The Radio Amateur Civil Emergency Service (RACES) is an organization of amateur radio operators who volunteer to provide radio communications for State and local governments in times of emergency. (These definitions came from the Virginia ARES/RACES site.) Some amateurs also support Skywarn, a National Weather Service program involving amateur radio operators trained to report severe weather back to the NWS.