I belong in the camp that says books should NOT be allowed. Some years ago I quit the Seattle Song Circle group over this issue. In fact, that last night, I even wrote a song about it:

"This is the song on page 17, page 17, page 17,
   This is the song on page 17,
And my book's better than yours.

This is the song on page 18 .... etc."

They were not amused ... probably because I ang it from memory ... bad bad bob