I use wikis fairly often at school. My first ventures out in wikiworld were really just pathfinders I posted for various research projects. After attending a CSLA conference workshop by Doug Achterman, I was inspired to make mine more collaborative. They were a good successful thing in our library this year. A freshman class or two made mythology wikis, 2 classes debated if Huck Finn should be banned, one class did a wiki on aspects of the Great Depression, etc..
I took several of them down but here are a few links
With these wikis I made the first page with tables, instructions and guides. I have found making tables with assignments already given works very well. At first, I tried to do my wiki-ness lesson by actually building first page with class in front of me. That, as you probably could predict, didn't work so well. Too many questions from too many quarters. So now I have assignment table prepared and just go over how I did it . (Sometimes I take the guides and instructions off when wiki is complete so students have a "finished" product.) I spend about 15 minutes showing the ins and outs of wiki- ness. The rest of the wiki the students make themselves. Sometimes the results serve as study guides, sometimes as discussion starts and sometimes just as products.
I learned how to put myspace backgrounds into wiki pages to liven things up!
All this image generating I am learning will really help.
I find wikis somewhat temperamental. A table I put in will look fine, but the next day will be misshapen somehow. I have a tolerance for non-perfection, but it really bugged some students.
Finally, for thing 17, I experimented with PBwiki's spreadsheet. I like this idea. I can see usefulness in students doing group projects where collecting numerical data is part of project. Also, I find many students don't know how to use spreadsheets. This could be a way to introduce them.