I have seen RUS used at the Getaway, usually with not very good results. But I'm sure even RUS could be used occasionally IF it was only used as a cue for words, and not to drone the lyrics off the page. Here's my succinct opinion, - better not to use a book or lyric sheet, but if you do, use it judiciously and skillfully. And better to sing using a cheat sheet than not to sing at all. I've seen a lot of people refer quietly to a printed lyrics sheet and still do the song admirably.