I have used Google Docs in my advisory class this last year to make a slideshow for the beginning of the year and 2 years ago with end of the year projects that student groups made. It was convenient for them to all be working on something and sharing and editing with each other.
I think that Google Docs is good for teams to be able to share ideas and add to without clogging up everyone's email inboxes. However, I don't think that I would use it to write tests on, as I still prefer regular word processors for that. Instead, I think the forms section would be a great way to do the exit ticket from class or a way to check students' knowledge of the unit you are studying in class. It would also be useful to get to know students' interests- I have an idea that I'm working on presenting to my principal for the year after next in regards to advisory classes.