Wikis are good for:

• Projects with limited timeframe and required lost of information sharing in documents (though Basecamp/similar might be better for many projects like this).
• Refining a shared text in a trusted group.
• Testing a concept on a vocal audience or market.
• Collecting dispersed knowledge (of certain types -- see [elothtes.pbwiki.com] for an example -- into a single document. Criteria: (1) evolving data/narrative, (2) no need for a final polish.

Wikis prowon't:

• Create community where it doesn't already exist.
• Provide a well-organized data structure or design. They're more friendly potluck tha elegant meal.