Here is a useful article on Wiki Myths and realities, which is a precautionary read for anyone tempted by a technology-led KM approach. I summarise their argument -
"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 Reaility - 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