A wiki seems to be a good means of communicating constantly updated information to a group of people. It invites the expertise of all its readers to contribute to its content.
However, it is a double-edged sword. The very openness of a wiki can allow misuse through members who choose, for their own reasons, not to be honest, objective or kind.
The library wikis that I've been reading about either have a limited group of contributors or else some form of special editing to remove inaccurate or malicious entries. Human nature seems to require one or the other.
I think a wiki would be a good way to plan an event without requiring the planners to schedule and attend meetings. It would also be a good way to invite reactions to proposals within a school system or library system.
An entirely different use would be having readers write reviews of the books they read for inclusion on the library website, catalog or other place (after some screening of the reviews).
The possible uses of a wiki are wide and varied.