OpenOffice.org launched its wiki in November 2005, and it has quickly become one of the world’s most-used wikis. (Number 16 on the top-57 wikis list. This is much higher than my Wikipages at the moment, but we are growing fast!)
I recently added a page for Quick and Easy Marketing Additions to help new users find things they can do to help right away. This is an example of how fast and loose editing, wiki-style, can invigorate online projects, and in the case of OOo, it certainly is helping to bring many new, informal collaborators to the project.
In fact, many FOSS projects have come to the same realization, and you’ll find wikis for Apache, Debian, Ubuntu, OpenSuse, Java, and many more projects on that list.