Google launched support for creating and managing revisions for arbitrary file types in the Documents List API. Prior to this, the Documents List API only allowed developers to create and query revisions of Google Docs files.
"This opens up the API for a number of exciting use cases. For e.g., a developer could use Docs as the cloud-based back-end for a content-management system with versioning. Another possibility would be for developers to provide file history or file playback in their sync clients.
Please note, however, that while all users can use API to query and manage revisions, currently only Google Apps Premier users can upload arbitrary file types via API. All users are still able to upload arbitrary files types via Docs web interface," explains Google.