No. I don't know of anyone who became commercially successful by singing a capella. (Except do-wop groups, which is not a tradition I much follow.) But I personally would never go back to playing a guitar; there are so many more rythmic subtleties without an instrument.

The best unaccompanied folk singers I know of are Scots; Jeannie Robertson, Ewan McColl, and Jean Redpath, in that order. Anyone who doubts the possibilities of this style should listen to some of Ms. Robertson's songs.

Shay Black is a magnificent a capella singer. And a very capable guitar player. But I cringe, and want to leave the room, everytime he cranks up one of his smooth, technically perfect guitar accompanyments and ruins another fine old traditional Irish song.

The most beautiful and exciting operatic aria I ever heard was on My Music. It was sung by Maria Callas, and Frank Muir was called on to explain why there was no orchestra for that particular performance. I forget the explanation, but for sure, she was better off without it.