I love wikis. I created a wiki for my bookclub. I created a wiki for my business. I've helped with wikis at work. I use wikipedia.
However, I have never used Library Success: A Best Practices Wiki. This looks like a good example of wikis can work well. Also, The Princeton Public Library Summer Reading wiki is a good example of a wiki working well. So much depends on those who are contributing to the wiki. If contributions follow a clear set of guidelines and the formatting stays the same throughout, then a wiki can be very useful. However, if if there is not a straight set of guidelines, a wiki can become a free-for-all.
Nancy Pearl's Booklust wiki has taken a turn for the better recently. For a few months, it was really a mess of contributions without formatting or proper organizations. It is now organized, and probably moderated, and no longer spinning out of control.