I once took piano lessons, but had forgotten everything except some very basic things - where C was, what a C chord looked like on sheet music, and duration of notes. Years later (oh alright - I think I was 18), I bought a banjo. I took a class and the teacher insisted on teaching us a bit of basic theory.

I have to say when I decided to play fiddle a short time later, I would have had a difficult if not impossible time teaching myself if I didn't know any theory. I had to learn tunes before I could play with people and the tunes on records just went too fast. I wasn't about to sit around practicing scales before I tried tunes when I could learn the scales and tunes at the same time. I bought a copy of O'Neill's and set about laboriously figuring out "So if middle C is there, that note it starts on is a D. It's got two sharps in it, so these are the notes I play...By Jinkies - that's a D scale!!!"

Anyone who dismisses ANY method of learning is eliminating possibilities and putting a big "Detour" sign up on the road to learning. The problem, I believe, occurs when people rely on one method only and that method isn't enough to fill their needs. It doesn't matter if the only method they use is learning from sheet music or tab, learning by ear, OR learning by the way fingers feel on the instrument - people need to have as many ways to learn as they can understand and use.