Entrepreneur.com's piece, "The Best Advertising Money Can Buy," relates some interesting points about word-of-mouth. (I have to admit, I'm a bit biased toward word-of-mouth because I think it makes perfect sense for libraries). In this article, the author discusses some techniques that hadn't occurred to me before. Namely, word-of-mouth is often generated by non-verbal offerings (like, the author notes, playgrounds at McDonald's). Letting your patrons discover your amazing service themselves, rather than telling them it's amazing, is important also.