The booklovers wiki maintained by the princeton public library is interesting, but there aren't very many reviews and most of the books that are reviewed only have one. It would be better if there were more reviews by more people, but that comes with time. For instance, there were only two science fiction books reviewed on the etnire site.
The Library Success: A Best Practices Wiki seemed to me to be more like what a wiki should be like. The booklovers wiki seemed more like a weblog while the Best Practices Wiki contains more information, still editable by anyone in the community, but less like a collection of opinion pieces. This was more like information sharing about practical and tried suggestions and ideas as well as conversation about certain aspects of library service.
I would think that a wiki like this would be very helpful for librarians. A quick and easy way to share success, pitfalls, and just general information with each other in a structured and organized environment.
The SJCPL wiki was a combination of the two wikis already mentioned, information about the county, and a FAQ about questions that get asked of the reference librarian. This seemed like a particularly good site for a SJC citizen as opposed to just librarians. I would think that a site like this would get a lot of traffic from the community and would be very helpful for people who might not be able to get to the library, people who have recently moved there, and people who might be unsure about what the library offers.