The online facilitation list recently had a thread about choosing wikis. The discussion included some pointers to the tools as well as some clarifying questions. The key in choosing the tool is the right fit to purpose and practices.
I have the great joy of working with Nancy White as guest editor for the KM4 Journal Issue on Technology Stewardship. The work of the editors is done on a wiki. So, I went poking around the wiki and I discovered this wonderful exercise she created to get people comfortable. I found the above image in Flickr under a license that allows me to remix it -- so I changed the title. I'm also reminded of Andy Robert's wiki on wiki facilitation.