Here is a useful article on Wiki Myths and realities, which is a precautionary read for anyone tempted by the idea that rolling out a Wiki will magically spark collaboration. The three myths they tackle are
"Myth #1: A wiki will heighten motivation and spark contributions
Myth #2: Employees will know how to contribute
Myth #3: Wikis will always surface the information you need
Wiki Reality -
many organizational wikis have endured only a very short life, with empty pages and almost no activity. Empty wiki syndrome typically results when a wiki gets implemented without a clear purpose -- without an idea of who it should serve and why -- or suffers from being too general by wanting to do everything.
A wiki offers a simple and flexible approach to creating and sharing information. Despite such simplicity and flexibility, a wiki project will not necessarily prove successful. Remember that flexibility also represents one of your largest challenges: You may gain a quick "win" for enabling collaborative content creation -- but this corpus could just as easily grow beyond your capacity for handling it".
I recommend you read the article - it's good, and is yet another reminder that Knowledge Management is not just about tools, nor even toolkit