We use pbwiki.com for our instruction wikis (which is totally free, you don't need to add anything...just sign up and make pages...there are of course enhanced options if you want to spend money). The faculty DO know about the pages because we advertise them in EVERY instruction session. We use them as part of our presentation. Each wiki page is a mini class/assignment specific library guide. We have also added links from our webpage to the instruction wiki. I think we are going to look into using Blackboard more heavily in the future (so we might try out the Blackboard Wiki tool then). I really like creating the wikis and you don't need to have coding knowledge to create them. I've also used them at my technical college, and the instructors who I've done them for LOVE them.
We require students to create a wiki as part of our Legal Research Skills Programme. The final part of this programme is an applied legal research exercise which students work on in teams of 4. They use the wiki to collaborate in note taking and to organise their work. We use Wetpaint wiki for this which is free and easy to use - so we don't have to provide instuction in how to use it. Students enjoy creating the wiki and generally use it very effectively. Sorry this is such a late response by the way.
I have started a wiki to introduce staff to library 2.0. I have not presented it yet, still fine tuning. This is my first ever wiki myself. But it is exciting. I used Wetpaint. It seemed pretty straight forward.