The power of wiki collaboration can be summed up in this Wikinomics graphics, originally created by Chris Rasmussen at US National Geospatial Intelligence Agency. For large enterprises caught in the mire of email and multiple copies of documents a wiki can be a godsend.
So why is it so difficult change behaviour. Take out wiki and replace with SharePoint and you still have will the tendancy to use email and separate documents.
Collaboration - Email vs. Wiki
From : Wikinomics Blog