Maybe the folks who have a difficult time memorizing lyrics are crippling themselves by relying to much on their books. I know. I'm one who has a hard time memorizing anything. The interesting thing is that after twenty years of working at it, memorizing lyrics is no longer the nightmare it once was. It may be that those using lyric sheets at jams might be preventing themselves from developing the ability to memorize efficiently.On the other side of the coin, it's sometimes fun to push your improvisational abilities and try a song you've never sung before! With the right folks, this can be very rewarding. With the wrong folks, it can be a disaster.
Mike