Ya, as Gpalmer was saying its not completely ludicrous-there may be something there (something above 20khz that actually lends itself to the musical experience). I gather there's not enough evidence yet to confirm it, again I've never searched out any original material on it (which may be interesting.) The only problem then is whether or not the rest of the audio chain, pre, pwr, dac, etc. is up to the job (not to mention a microphone capable of recording up there). I wouldn't say the tweeter is for "dumb" people, I'm not sure what your friend means or knows by it. I believe something like 1% of the population can hear up to 25,000hz. I wouldn't expect any massive changes soon though in speaker design, most of the designers are still working on how to get up to 20khz perfect. At best though I would imagine its level of significance being something debatable like stereo bass being audible (the latter depends alot on the room).