Keeping in mind the principles of sound professional development first (starting with a quality long-range plan)...
It is tempting to have everyone sit in a classroom and have one individual demonstrate wikis via the LCD. A better option providing hands-on experience is to pose the following scenarios before professional development time:
My middle school team needs to plan our cross-curricular "Environment" unit. We need to make sure we coordinate our lesson plans to fit in the field trip as well as the project fair day. We also need a way to discuss how our lessons have a cross-curricular impact that other teachers can pick up.
In my science classroom, my students need to create a study guide to prepare them for the test on potential energy vs. kinetic energy and simple machines.
In my 5th grade classroom, we would like to enhance parental communication, parental feedback, and parental involvement. In addition, we'd like to have parents share their talents/skills/experiences with our students.
We need to plan a community-building potluck for the inservice on February 13. We need to A) brainstorm what to bring, and B) determine who will bring each item. But we don't have time for a meeting, and "reply-all" email is too messy.
Use these scenarios to highlight some of the dilemmas that we face in terms of coordination and collaboration. When you address the staff, you can make mention of how we often think of wikis as Wikipedia... that is, an editable encyclopedia. But really, wikis are so much more.
Next, set the staff loose. Have staff who have never experienced wikis before start at the Wiki-Walk Through. This site does an excellent job of explaining the what, the how, and the why of implementation, giving examples in a number of subject areas.
Experienced staff can look at the Wikipatterns website instead. This website highlights numerous strategies to encourage more wiki collaboration, which is perhaps the top frustration for teachers who have used wikis in the classroom.
Regardless of the group, have them add the new thoughts they learned and ideas for implementation on a separate wiki. Encourage teachers to add to other people's thoughts, or pose questions for each other. This will give the inexperienced the chance to practice editing, linking, and saving, and all teachers will be able to see how ideas can be interwoven.
Bringing the group back together, you can talk about how wikis can be used to address so many more things than just building an "encyclopedia". Today, we used the above scenarios and had some volunteers play the part of the teachers, students, and parents that were collaborating. Their example is here.
With each time you look at 21st century tools, it is important to have an agreed-upon list of principles of quality teaching to refer to. For example, Will Richardson's list of shifts in education would work well. Wrapping up the session, you can run through the list, showing how wikis serve as a 21st century teaching and learning tool.