Comment Thanks to John Kozubik, rsync.net, and Ken Loafman (Score 1) 384
Duplicity is the right answer, as I have posted elsewhere, and we owe great thanks to John Kozubik and the rsync.net team for proposing, and sponsoring, the continued development of duplicity:
http://www.rsync.net/resources/notices/2007cb.html
Prior to that bounty, duplicity had not been updated or worked on for a few years, and thanks to the claimant of that bounty, Ken Loafman, there is not only a new, stable version, but a responsive community working on the project.
I use it every day, and now consider it indispensible.