Wikis in Libraries

Matthew Bejune's article "Wikis in Libraries" in the September 2007 issue of Information Technology and Libraries takes a look at the use of wiki technology within the library world.  Matthew identified 33 library wikis and placed them in 4 categories (see examples of all four wiki types at LibraryWikis):

1. Collaboration among libraries (45.7%)
2. Collaboration among library staff (31.4%)
3. Collaboration among library staff and patrons (14.3%)
4. Collaboration among patrons (8.6%)

So, why are wikis used predominantly for collaboration within libraries? 
Matthew provides several explanations that include the personal characteristics of information professionals.  Librarianship attracts service-minded individuals who are interested in helping others,  whether they are patrons or colleagues.  Another explanation is the role of library associations such as the SLA and the work that is done through these associations throughout the year.  According to the author, "Libraries use wikis to collaborate intraorganizationally and extraorganizationally because collaboration is what they do most naturally."

How many of you make use of a wiki and how is it utilized?  Which category does it fit into?