I am a self taught guitarist and, although I say it myself, have reached a fairly high standard of playing, incorporating a number of different styles. The problems with being self-taught only became evident when I started to branch out into other genres, in particular, jazz.
I played for a number of years in a gypsy-jazz trio, often fast and furious chord changes, and not a straight forward open chord amongst them! I had to work twice as hard as the other guys to learn the pieces and quite often found out later that I was using a wrong chord here or there simply because I hadn't learned how to work out the theory.
Not many people pick up the guitar with the intention of becoming a great player. Most folk would be happy enough to be able to strum a few chords and sing along and that's great, but if you really get the bug, then some time, later on, you're going to wish you had some musical education.
I've had to turn work down because I knew the other guys expected me to turn up and play anything from their pad at first sight.

My six year old daughter is presently having piano lessons, which I take her to and wait for her. Just now, it's very basic stuff, but as she progresses it's my intention to be watching and learning over her shoulder.