I've been exploring Tom Barrett's web site and came across this presentation on using Google Docs. Wish I had seen just the first two slides before I attempeted to teach a collaborative document to the kids. In case you don't know there are limits on the number of individuals that can collaborate at the same time. I believe it is around 10 for a doc. Barrett points out it is 50 for a spreadsheet. So, an entire class can practice working on the same document at the same time.
Once again lots of good ideas. You should be able to find at least one you could use in your classroom.
[image captured from "twenty one interesting ways to use Google Docs in the Classroom"; http://docs.google.com/present/view?skipauth=true&id=dhn2vcv5_8323t58h3ft]