My first thought on Wikis is that Wikis can be used for group projects. Students can post their contributions to the project and edit the project at the same time. This works particularly well for larger groups that might otherwise have trouble finding a convenient time for everyone to meet. With a Wiki, students can add their contributions at any time that works for them, and everything is nicely kept in one place. No paperwork to lose or misplace, no tedious handwritten changes --- no emails that get deleted accidentally.
Like the example showed, Wikis can be used for anything, not just school work. Fabulous!