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 http://elothtes.pbwiki.com for an example -- into a single document. Criteria: (1) evolving data/narrative, (2) no need for a final polish.

Wikis won't:

• Create community where it doesn't already exist (or can be easily defined from existing networks).
• Manage conversations as well as a blog or other technologies.
• Provide a well-organized data structure or design. They're more friendly potluck tha elegant meal.

Pros

• Informal and unmonitored
• Public, to at least some degree (people take public content more seriously)

Cons

• Users do not write, edit, design, or create navigation with consistent rules--even if you try to set them out at the beginning. This is because people vary in how much they _care_ about structure and consistency. (The "Odd Couple" effect.)
• Poor writers and people with trite ideas _do not_ necessarily realize it.
• People whose skills or knowledge are superior often want this recognized--the best and brightest may be the least likely to contribute to a wiki.

Good reading

http://del.icio.us/hrheingold/wiki