I'm afraid I have to be to voice of dissent here. I agree somewhat with much of what has been said but I believe the audience isn't paying to find out how well we've memorized the words and music. They want to be moved by the song. Because of that any form of cheat sheet is acceptable as long as it is not a distraction. Lou and Peter Berryman work with a 2" binder open in front of them. I remember Rick Fielding at Mystic working (in a workshop) with a binder on a little stand at his feet.

I agree we owe the audience a level of professionalism but that level need not put at risk the reason they are there. They are there to join, in empathic bonds, the singer. They want to be transported by the song. Some of you may be such good instrumentalists that the audinece is there in awe of your ability with your instrument but ultimately we owe it to them to make them happy they walked through the door and paid their money. To that end any technique that works is acceptable.