Most people think of wikis as user generated content, but these are also handy for documentation projects where there are few authors but many readers. Most good documentation has two types of content: specifications and examples. The specifications explain how the thing works and are "locked down" as changes are restricted. The examples section is more free-flowing and it is desirable for users to add their own examples. The nice thing is that MediaWiki can be used for both. For specifications you can protect pages so that only a select group of users can make changes to them while at the same time leaving the example pages untouched.
Using a Wiki to Reduce Support CostsIn any product, a support call or email is typically "how do I do X?" and the user may or may not have actually tried to research the problem first. When receiving a request like that the knee-jerk reaction is to explain to the user in a response how to solve the problem. But that only works that one time, and the next time that someone has the same question you'll have to answer the question again. Now many companies turn to user forums, hoping in vain that users will search through the forums for the answer before asking again. But few do, as forums are often full of questions and rarely full of answers.
The better way to answer a support question is to answer the question by creating a Wiki page. This has several benefits. First, the next time that someone asks the same question you can answer the inquiry by sending the user a link to the article (whilst also kindly reminding him to RTFM first). Second, it's a little easier to find a Wiki article due to the organization and searchability of a Wiki site. Finally, it encourages others to add on to the page, increasing the quality of the answer.