This will be another short one because I've already covered it in CamMed23. since that post I've been using wikis as part of planning the (lib)TeachMeet(have you signed up yet?) and at the medical library for putting together the answers for a quiz. I still think the most obvious use for wikis in a library context is internally for staff manuals and shared information.
And again, if you haven't visited it yet check out the #camlibtm wiki!