Based on this great blog post by Tim McCormack, I managed to write some scripts that back up files to Amazon S3. The files are encrypted with GnuPG and rsync-ed to S3 using a Python-based tool called duplicity.
designed to manage user specified directories referred to as sync targets from here on out, in tmpfs and to periodically sync them back to the physical disc (HDD/SSD)
C. Morbidoni, G. Tummarello, O. Erling, and R. Bachmann-Gmür. Proceedings of the 6th International Semantic Web Conference and 2nd Asian Semantic Web Conference (ISWC/ASWC2007), Busan, South Korea, volume 4825 of LNCS, page 533--546. Berlin, Heidelberg, Springer Verlag, (November 2007)