I've been using duplicity for a few years now and have been quite satisfied. It did seem slow when I first started using it. I learned to live with it; you run backups overnight anyways.

From what I can remember, a lot of the slowness came from GPG, and specifically files being compressed before encryption. Disabling compression speeds things up, but trades off disk space (and security).

I wonder what it'd take to reengineer the thing to take advantage of multicore -- being CPU-bound on a single core is I think what makes it slow.

After having a look at duplicity [1], it actually reads as pretty decent. I still wonder why research is needed for such a thing, instead of Cannonical taking it, installing a good default script, adding some GUI in their installation image (choosing your sftp backup target, username, password (managed by keyring)), so everyone would already be on the right path.

[1] https://help.ubuntu.com/community/DuplicityBackupHowto