Really? I don't think needing or wanting a cribsheet necessarily indicates a performer doesn't know a song. Performance anxiety and what happens in the brain with age can both lead to lapses of memory - no matter how well a person may have learned the song.

I suppose there comes a time with even the most well-known and applauded performers reach the point through the aging process when they really ought not be performing in large venues anymore or expecting people to pay big bucks to see them. (From what I have recently heard, BB King comes to mind - but that goes well beyond using a cribsheet for the lyrics.)

I agree that a paid performance is not the time or place to learn a song. I don't think using a cribsheet is an unforgiveable sin, however, and don't think some one using a cribsheet necessarily, even usually among celebrated singers, suggests they are "learning it on our time." Not saying it has never happened. But hard to believe a singer who is celebrated can be routinely accused of learning their songs on our time.