I especially like the opportunity for library users to contribute to book reviews and enhance the service the library can offer - librarians would never be able to keep up the quantity.
Great potential for guidance for parents regarding reading suggestions, high school students for resources and suggestions for study and of course their very own wiki for reading recommendations. http://thepulse.org.nz/Read/
Another way of using them which seems to work well is for consultation,e.g.
on digital strategy.
Of course there is an assumption that contributors have a certain level of expertise - there can be the downside of a variation in knowledge and presentation and it would be a better service if it was mediated.