It would be interesting to combine this with Google Gears for offline storage too. Tougher to create something that securely shared data between users, but for a single user this could still make some powerful apps!
This is a neat trick, but not very flexible or scalable.<p>Basically each user is given a presigned authorization token that lets them upload certain files to their bucket. Other users only have read access to the <i>index</i>. The clever trick is that the <i>key</i> is used to store the publicly available data like the latitude and longitude.<p>It works out well in his case, but it's not very useful generally.