The first time I encountered a singer carrying his little boom box onstage to provide accompaniment, I was very dismayed and taken aback. The artist was a favorite or mine, and a truly great vocalist: Aaron Neville, who normally performs with a band including his three brothers and a few additional musicians.

Aaron can play some piano, reporetedly, but does not do so onstage; he is a vocalist who relies on accompaniment. The event was a benefit of some kind and I believe that Aaron wanted to contribute his services without having to coerce anyone else into appearing to back him up.

The set was fine, of course, if a little strange.

I agree that "canned" accompaniment is inappropriate for most any kind of folk festival or concert, and that in almost any context, it carries a whiff of unprofessionalism.

Now, "looping" to achieve some kind of one-man-band performance ~ that's much more OK with me. One very talented guitarist who performs at our local mostly-acoustic coffeehouse does a solo electric-guitar act wherein he plays a few measures, or even an entire verse, while recording it, and then (immediately and seamlessly) allows it to repeat while he plays over the recording as it replays.

And then, taking it several steps farther, there is the incomparable Theresa Andersson:

http://www.youtube.com/watch?v=C8Li-DaJny4

http://www.youtube.com/watch?v=z8xx6xKKJ6A&feature=channel

May not be "folk," but it sure is music!