But S3 doesn't even have "folders"; a bucket is just a mapping from keys (paths) to values (documents). So if you want a document at /foo/bar, just store it at the path /foo/bar.

The only special case is the root "folder" (i.e. the empty key), which CloudFront does now explicitly support: http://aws.amazon.com/about-aws/whats-new/2010/08/05/cloudfr....