I've used Obnam a little bit. Now that 1.0 is out I plan to replace my duplicity backups with it. I've been finding duplicity to be rather creaky, and the times I've needed to restore a few files have been painful. I need encrypted offsite backups, and Obnam's killer feature for me is supporting that.
Quite a lot of care has gone into Obnam's use of gpg too. It doesn't just encrypt data to a single gpg key, which would prevent changing keys later without reencrypting all the data. Instead, it encrypts data using a secret key that is itself encrypted by your gpg key(s). So new keys can be given access. The scheme is explain here: http://liw.fi/obnam/encryption/
I liked that so much I implemented the same scheme in git-annex for its gpg encryption.