The best learning curve I ever got on to was to sit in as rhythm guitar in a Django/gypsy-jazz band. Aside from having lots to think about with the unusual, and pacey, chord movements, I had to learn to listen and to get behind the melody lines and solos of the lead guitarist.
On a good night we could really swing, heads up and watching each other for cues and clues as to where we were going next.
My time spent playing in a purely supportive role taught me more about presenting music than all of my years of playing.
I've enjoyed reading this thread. I don't know how I missed it first time around!
C-flat.