Last year I watched a College of DuPage "webinar" (at least I think that's what it was) that introduced PBWiki. We started a staff wiki at our library to help keep everyone informed without having to post notices, send emails, etc. Each department has their own page, and we've linked lots of useful information (staff phones, committees, equipment troubleshooting tips to name a few). It's handy to be able to check on news when I'm on vacation or at home, too.
I really like the Wyoming Authors wiki and the Best Practices wiki - I see there is lots of useful information there (like gaming in the library!). There is always the risk of someone editing incorrectly or posting false information, but overall I think wikis are really handy.