The ARRL (American Radio Relay League) has a whole bunch of technical stuff on their website here . More than you'd ever want to know.

It's a neat technology, with a flawed specification. Normal AC current in the U.S. is 60Hz. One little slice of the huge electromagnetic spectrum. Easy enough to avoid. With BPL, multitudes of frequencies are used, their distribution depends on the BPL technology used, resulting in a splatter effect.
A HomePlug conformant in-building BPL system actually has "holes" in it's specification to prevent interference to amateur radio (and probably other government HF operations).

A whole slew of entities haven't just said no, they've said... well, you know... <img src="images/graemlins/smile.gif" alt="" /> We'll see in the future if the FCC is more concerned about money, or radio interference to existing licensed users.