I've found the Amazon S3 functionality to be fairly lacklustre to be honest... Set up an incremental backup to run every night at midnight and have my DNS 320 set to turn off at 8am.
After the initial backup, all it seems to be doing is overwriting the same files every night, so the backup never grows as you would expect it to...
If you're expecting any other functionality apart from S3, then I'm afraid to say you've just bought the wrong NAS...