Hi Joël,
I have some experience with this through the REST API. We used google docs as a storage solution for files generated by Mendix. The customer could also upload files in google docs and Mendix could retrieve them.
In my experience this was a nice solution, it worked good in combination with the google authenticator. Furthermore the options of google docs with authorisation are nice.
In our case there was no need to edit the files from the Mendix application, so i dont know what the possibilities are. So from my perspective Google docs can be used as a nice document storage tool, not sure about the editting option in combination with Mendix.