Without even looking at the wikis, I started thinking of ideas on how I could use them. We have a lot of hands-on building projects in my physics classes, so the students could pass on helpful info from one year to the next. Ideas on what make the best wheels for a mousetrap car, or where to buy the right springs for a catapult, etc.
We could also use them as a place where students can explain the subject matter to others in their own language. A student masters a particular subset of info, and relates it to both their class and future classes using a wiki written in their own language.
The biggest hurdle I foresee is the continuing problem of access to resources for some of my students. Ideally, students would need computers with internet access available before and/or after school, which my building does not provide. There is a computer in the classroom, but only one, and I can see traffic jams building up from here.
I think if done properly, a Wiki could be a good idea for a yearlong class project. It's one of those ideas that will be extremely rocky the first time out, but will hopefully get better year after year.
For the record, the Wiki that I liked the most was the Flat Planet site exploring environmental issues.