Dick's the man.This ties in to some discussions we have had about confidence in one's abilities, or lack thereof. All singers make mistakes, forget lines, screw up the order of verses. The professional way of dealing with this--aside from trying to practice before the gig--is to think fast on your feet and don't apologize or stop and start over. Have a turanaround you can play while you're trying to figure out what to sing next.
If you know you'll have a problem with a song, its good to have a minimal cheat sheet, like just the first line of each verse, at your feet. (AT YOUR FEET, in BIG LETTERING. Rustling paper and going through messy binders is also unpro--and I should know.)
Willie-O owner of messy binders.