I just completed Lesson 5 of the Learning 2.0 program-- about wikis. I am so far behind on this project! I need to get several lessons done ahead of time and just post them at the beginning of the correct week!
Anyway, my thoughts on wikis: Many library technical services departments have used them to post policies and procedures on a website that everyone can find. It's easier than making a web page another way. Betsy started one, at http://dupontlibraryrms.wikispaces.com/ and posted a couple of documents on it. We need to add more things and update a lot of our procedures.
We have had a library wiki for news, but it's on a different platform, Tikiwiki I think. I think it's a little more difficult to use.