I had never used a Wiki until last year in Young Adult Literature. When I found out that the Wiki participation was a large portion of the grade, I literally groaned. But once I got the hang of it, I loved it. It is a great discussion tool! We had a page for each book we read, and we would log on and post our opinions about the books. Publishing our name with the post was optional, so many people were very candid. The professor closed the wiki to just our class, so you had to log with a password to participate. This is a feature that would be necessary for public school use.
I am not sure that I would be able to use a wiki with my little ones in the library, but this would great for a secondary librarian and a book club. You could set it up just like my professor, a page for each book, or maybe a page for a set of chapters depending on the age of the students, participation, and the content/theme of the book. I know the older students would love to see their opinions published online!