I think the best use of a wiki I have seen is the method Leo Laporte uses one for his show notes. He give out the login information on his broadcast and allows listeners to add to the show notes. The result is a much larger pool of information on the topic. This is, in my humble opinion, collaberative KM.

I still listen to his podcast from time to time and have never heard him say anything but positive on it's use. I don't ever recall him commenting on any spam problems or such things.

I wish that more organizations would adopt such ideas. At my current job, my work inbox is always flooded with seminar announcements. It would be so much better if a calendar wiki could be created. This alone would save each employee the task of opening each message to get the information. There are, of course, many other ways such items could be applied.