Wikis can be used to collaborate with other librarians, teachers, as well as students. One of the problems that I may see is that our district has such secure webservers that it may block usage. However they can use it at home for projects such as vocabulary words.
Currently I am taking a YA lit class and we use a wiki for posts on books that we have read. I have enjoyed reading what other users have contributed. I also love the simplicity of the site.