I trained at the wiki station at HCPL's Technology Fair, so I know about wikis and what some libraries are doing with them. In addition, I edit and update a wiki for a YALSA committee that I am on. I also volunteered to maintain the wiki for the new ALSC committee I am serving on.
Wikis are a good idea when people collaborate on them. I have seen wikis where there is no collaboration and just information... like a web site. There are some wikis that are basically just web sites, and I think many use wikis for this purpose since they do not need to learn html or any other programming language or they do not need to pay a webmaster to do the job.