Well, if the Sandbox Wiki taught me anything, it's that you really need someone to build your Wiki first before calling in other participants, otherwise it had no real goal. And a wiki without a goal just turns into a bit of a mess. A literal pile of information.
I really enjoy Wikipedia, it's a very clever idea. I've heard it's actually the best source for information on *ahem* government projects because "official" sites won't disclose as much. haha. Not sure if that's true. I tend to use Wikipedia more for fandom related issues. While I tend to double check anything "true", when it comes to checking the facts about the last Harry Potter book or characters from Star Wars, Wikipedia has your back. I did a manga program earlier this year, and I used a lot of the information I found on Wikipedia to create trivia games for the kids to play.
I'm impressed by how well managed Wikipedia is. The "staff" edit content and check entries to make sure they are written in a objective manner. (Though it's wise to double check with another source, since you never know who the last person was to edit the entry.)