Media Mover 2's S3 implementation now supports private files hosted on Amazon. You can set access to files by role- with the obvious exception of the anonymous user. Links to each file expire after a set amount of time which gives site administrators a degree of control for providing protected content.
Currently the implementation supports uploaded files via Drupal's upload module and Media mover files that are displayed on XSPF playlists. The upload module implementation unfortunately uses phptemplate to override the non-protected url. In Drupal 6 the ability to override the file path is limited which prevents a more abstract solution. However, it is easy for themers to integrate the protected URL in their templates if you are not using the standard file attachments theme function. Additionally, the Media Mover S3 module provides a way for themers to check to see if the current file has been moved to Amazon or if it still only available locally.
