I'm not a big wiki fan. As an educator, I most certainly wouldn't let my students use a wiki as a legitimate source for research. They may be useful for professionals to put together ideas of resources or answer reference questions, but the user must still determine whether the information posted is credible. It's too easy for my comfort level.
I also agree that a wiki is only as good as the people adding to it. Unless the information is relevant and organized (as our 23 Things wiki wasn't) it can become just a jumbled mess of useless information.
I also found it interesting that during the trivia contest this year a team was discovered changing a wiki so that the answer was not available for other contestants. Too much ease in causing trouble is my thought.