[oxoxo]

no it's not a automatic upload to s3 server. You can synchronize with external tools your attachments every night. Or you select your favorit attachments and copy manuell to your s3 server.
The attachment.php take the attachments first from s3 server and when not found, then take the attachment from your webserver.
Best practice, all thumbs leave on your webserver and copy the pictures and attachments to your s3 Server.
Next Version, we should built an configurable cron job, which synchronizes the attachements and after synchron job run, should the job remove all these attachments from webserver.

The VBS3Uploader Tool upload your new Attachments directly to your s3 server and save the Reference in your VB Database. After Upload you can select the Attachment for your Posts in the VB Software. Alltrough the attachment is not on the webserver. Its only on s3 server.