Out of interest I had a go at building a Data Sync provider that we could use to backup our Website content to Amazon S3.
It turned out to be pretty simple using the Amazon SDK, there's a couple of gotchas that cause a little trouble as we can't set the modified date of a file in S3 so instead we add some custom meta data for Created and Modified which in turn hurts our performance on the read. We have to issue a web request for each file's metadata to return the modified and created dates. Good news is that if you're not that worried about that you can remove them from the schema map and just rely on the Length of the file for change detection.
Download the provider from here.