It seems as if 6 string electric baritone guitars have been around awhile but what is the advantage, sound, etc of this guitar? Does anyone famous play one? Has one ever been used in a popular recording?
Dave Matthews played one on quite a bit on Everyday. Here is a link mentioning it.
Lots of nu-metal guys play them. They detune the crap out of them (think drop-A tuning) for an ultra-bassy growl. The thicker strings support it. Lots of them also use a 7-string guitar for the same reason.