I find some of the poorest acts in a sing around are those who read the poems of others. There is always that feeling that if they learnt them the presentation would be so much better. I know Les (and the Coppers) use books - but it always feels like part of the act.
However, I have to admit to using a booklet when it comes to Xmas songs and carols - I only play them one month a year. I never remember verse three and beyond, and my copy has useful bits of notation like SN; start note.   
FloraG