I would say that one of the best features Wikis provide for writing courses is that students can see their progress. Every change they make to their page is registered in its history and nothing is ever lost (if saved properly). Students start by writing a draft, then revising, after that they can go to their page with a classmate and they can both revise it together; the student might work on it with the teacher at a student-teacher conference, and the process can go on and on until the student and/ or teacher is/are satisfied with the piece of writing. The student can go to the first version and see how it has changed, identify what mistakes he had originally made and appreciate his progress.
Wikis can also work as online classrooms where there can be a main page with the syllabus and links on the sidebar for the activities for each week, tutorials, collaborative exercises, other external class sites such as blogs, bookmarks, aggregators to keep track of several sites simultaneously, etc. Pages can hold videos, slideshows, chat boards, images, hyperlinks, voice threads, in sum, anything that is embeddable.
I have already mentioned a wiki we had in our last EFL writing course where the main objective was reflecting on EFL writing, what it meant, what it involved and how to get more self control in order to learn to revise one´s texts, revise that of peers, write for a real audience beyond the teacher and even beyond the classroom through collaborations with EFL students abroad, etc. Here is an example of activities for a given week, materials needed and the weekly list of benchmarks.
The tool my students always find the most useful is the chat board. There, all members can communicate with one another, ask for help, send quick messages and write their ideas in a few words. Every message is recorded and students can go back and re-read instructions, previous threads, etc. The chat board we use is Cbox, a free tool that can be embedded in wikis or blogs.
Something that happens to me over and over again is that whenever I start using a new tool, it is very difficult for me to change to another. I started working with wikis in Wikispaces and although colleagues have mentioned the benefits of Pbwiki or Wetpaint, I stick to Wikispaces, even if it has ads on the right sidebar. The same with blogs at Blogger. I have tried Wordpress and Motime and Blogger is still the one for me. Does this happen to you too? or are you more flexible and adaptable?