I use it to save backups of my desktop and laptop home directories to a home NAS mounted with NFS, which later gets synced to another NAS.

It's a decent tool. I encrypt with a separate gpg key, do mostly incremental backups, and a full one every few months. Incremental backups take under a minute on my desktop (100K files, 11G). Full ones are kind of slow (which is why I set it to only do it every few months).

I haven't used the S3 support.

I use it to keep incremental backups of my VPS. It lets you use S3 as your backup destination and uses GnuPG to encrypt all files.

Have used Duplicity for a couple of years now, works very well although tricky to get it to store data other than in the US-East region. Currently backing up about 8 servers with it, mix of Ubuntu & Amazon Linux.