I got attracted to this idea because it offers several security advantages. I've been working on a minimalistic javascript library (byoFS.com) that allows you to connect a Dropbox/Google Drive/etc. account and write automatically encrypted data to it. I tied for 2nd place at a recent privacy hackathon for making an encrypted chat application using only Dropbox accounts:
I actually tried to do something like this for a Comic Book reader, but the Dropbox API didn't allow for file requests to be made through JS: http://rkuykendall.com/articles/web-slinger-comic-reader/
With datastores, the changes are automatically merged according to developer-specified conflict resolution rules.
Interesting to note that the datastore isn't really deleted when one revokes Dropbox access to the app, even though it's no longer listed on the datastores page - relinking the app to Dropbox resurrects the previous data.
