My experience with wikis is very similar to Diane’s — the company I was involved with (previous to my work in the library field) decided that the best way to document procedures and methodologies within our department was to introduce and make us of a wiki. To say that it was a failure would be kind.
When you take a look at Wikipedia, it has a look and feel that is consistent throughout — standards, as it were. I think this is critical for collaborative websites, particularly when business is involved. This was not thought of, nor administered, in this business wiki. And, simply put, it was not mandated within the corporation that this must be used, so people didn’t use it.
This having been said, having a collaborative approach within a group is an awesome way to get knowledge out of minds and onto pages, if properly supported.
Pre-Superbowl, I will be making some changes to a wiki page involving the Town of Lincoln, on which I’m a Councillor.