Ran across an article for the GnuRadio project, an open-source software radio implementation. One of the most interesting things was seeing a spectrum plot of the radio frequencies between 0 and ~450kHz, and which ones are used and unused.
The theory of a software radio is you could put a single, fairly simple chunk of hardware on your computer, and at that point it could transmit and receive pretty much anything -- walkie-talkies, AM/FM radio, GPS, HDTV, you name it.
All of a sudden a few geeks have scared the crap out of the FCC and MPAA. The FCC because, well, airspace is their turf, and the MPAA because they see control of transmission mediums as a way to prevent "piracy".
Anyways, the spectrum plot is interesting because, among other things, it shows how little of the existing broadcast spectrum is being used in everyday life. Software-defined radios are already here in a number of commercial products -- we'll see if open-source SDR results in cool new tech or nasty new leglislation. Or both.