I guess I have the ability, after many years, to play "totally by ear". I play my ipod on shuffle and when something interesting comes up I pick up the guitar and can play along with no thought as to the key or scales etc. I think more in terms of intervals and melody than theory. But, of course, that's because 50 years of experience is telling me what to do.

I've been told I have good ears, and its useful. People often call me to sub for somebody on a gig and I can usually hang in there without rehearsal.

But that's not something you want to do all the time. If you're going to play interesting stuff, you've got to be aware of all the possibilities and that requires a little more thought and analysis.