One of the librarians at MY library has created an often-asked questions reference wiki, as well as one for homework assignment. These have been for staff use only as the url was posted only on a staff intranet. However, when our "Useful Links" page dies, and our del.icio.us account takes its place, the wikis will be more accessible, although I am not sure how they are tagged.
Wikis seem anywhere from very easy to mildly complicated to create and edit. and of course each one you have to look at the sometimes unspoken protocol, when you are going to edit. Are things in alphabetical order, do you delete and then post updated content, or do you post underneath or?
In some ways wikis are/can be like the stenographer's book at the reference desk, where people use to write important things that they wanted all to see. Of course they can be much more, and some brave libraries probably allow their patrons/customers/clients/stakeholders to edit.