The "out of tune" posts above reminded me of a radiothon that I did many years ago. I had been playing the guitar for a tune in Bb. The next tune was I Saw The Light in G and I played the banjo. The fellow who had been playing banjo handed it to me and took off the capo, but left the fifth string tuned to Bb. It was obvious that something was wrong when I started the intro.
These days I'd stop, fix the string, make a joke and start over, but being very nervous and inexperienced I continued playing. By the time I got to my break, I'd discovered the problem and fixed the tuning of the fifth string, but the intro sounded terrible. I still have a tape of that show. I hope no-one else has.