David Jakes, in his article "Wild About Wikis" states that:

"Simply put, wikis enable anyone and everyone to create content online using easily understandable tools. The most famous wiki is Wikipedia, an online encyclopedia created by users from around the globe. Wikis are also increasingly being used by the corporate world; for example, eBay recently added wikis to its auction site so members can coauthor articles about buying and selling. Not surprisingly, K-12 schools are also taking advantage of the opportunities for "collaborative construction" that wikis provide. "

Here are some resources on the subject:

Articles

Tech for Learning

Educational Uses of Wikis

PBS Teachers

EduWikiTutorial

Wiki Walk Through

What is a Wiki? 

Wikis in the K-12 Classroom 

Wiki Ideas

Learning With Technology

Carolyn Foote's Wiki Presentation at TCEA 2008

Videos and Slide Shows

Commoncraft

Telling the New Story 

PBwiki Educator Videos 

Why Wikis? 

Educational Wiki Examples:

Room 15

Penn State Class

GCSE History Wiki

Mrs. Lowe's Class

Arbor Heights Elementary 

Valley View Library  

Holes Wiki

Room 9 

Mrs. Browning's Class: Texas Regions

The Aristotle Project 

Terry the Tennis Ball

Westwood Middle School

Grade One Classroom Wiki

8th Grade Science Collaborative Wiki

Lesson Plans

Math Wiki

You can set up your own wiki at:

PBWiki

Wetpaint

Wikispaces