As a relative novice, I have to disagree with Racer. I went nowhere playing the guitar until I started to learn even some rudimentary theory. Even knowing what keys are, that most songs have a I-IV-V7 format (or the equivalent) and that there are natural minors, puts hundreds and hundreds of scattered bits of information into order, let's you memorize songs 100 times easier, and makes it easy to figure out what a capo can do for you, and that one song shape with chords can be in another key and changed over. This is about half an hour's serious work to learn. If I had even those rudiments twenty years ago, I would have saved immense amounts of wasted time and grief. People learn things in different ways: but a very little theory goes a very, very, very long way.

yours, Peter T.