My class has been using a wiki regularly since the beginning of the year. They are now (mostly) competent at linking to pages, adding content and editing pages.
We run into the occasional problem such as someone accidentally linking to an already existing page and proceeding to delete all content!! But in general I am incredibly impressed with the skills they have gained in such a short time.
I am now seeing these skills transferred. One of the students in my class has now gone on to create her own wikipedia page. Remember these kids are 9 and 10 years old!
The most positive outcome of using a wiki is the fact that all of the learning that occurs is authentic. It serves a purpose. There is always an audience -- a huge audience!!
Please check it out at http://pohutukawa.wikispaces.com