I like the idea that you have access to all of your revisions. Too often students revised something and it is not really better. They might want to go back to the original one but they do not have it saved. This way they can go back and see the progress they have made. It is also an easy way for others to help with editing.
The jackpot: this guide contains lots of links for practical applications of Twitter, Wikis, GoogleDocs, 3D virtual worlds etc...in the language classroom