I've heard the term "Nashville tuning" used in reference to stringing up a six-string guitar with the octave-higher 12-string-type strings as substitutes for the four lowest strings.

Apparently, studio players on Country Music Row have used guitars with this setup for ensemble playing -- in combination with one or more other 6-string guitars strung in the standard manner,adding one of these "high-strung" instruments creates an extra-complex 12-string sound.

Any thoughts on the electric twelve, a la Roger McGuinn? (Yeah, I know -- that's not his *real* first name...)