I've been thinking about backups again. I always have the crazy pipe dreams of removable hard drives, cycled every day (expensive), or the slightly more realistic thoughts of tape drives (lacking in capacity). What about the sometimes-explored online backup method, though? For argument's sake, I'll assume several people want to share the backup load, backing up others' files in exchange for others doing the same.
Rsync has obvious potential here, as it's very good at being incremental and can be tunneled over SSH. This method would require either: a centralized point of storage for all clients to upload to and download from; or rsync access to each machine that needed backing up. Not bad, but there's another method I like a little more...
Picture a nightly backup tarball, encrypted and signed for security. A .torrent file is uploaded to a tracker and simultaneously handed to the backup peers. The peers download the tarball from the tracker and from each other, and we end up with our redundant remote backup.