I have used wikis before as a shared workspace for a group project involving staff from Rodney and Waitakere Libraries and from Datacom - it was a good solution for a working group that was geographically spread not only across Auckland, but across NZ (one member was based in Christchurch).
The pros - it was a good one stop shop for providing overall management of the project, and also as a home for recording decisions once they had been made. It's also a good place for setting up frequently asked questions.
The cons? For some members who didn't use it much, having to log in each time (and remember their log-in) and then remember how to edit was too much of a barrier to its regular use, and most tended to revert to email for the day to day correspondence. The other negative - becasue it's web-based, it's fine if you want to link to other web pages, but not ideal as a repository for large project-related documents stored on local drives.