I am a fan and user of AFS, the Andrew File System, and I run an AFS cell on sarna.org.
For an introduction to AFS and what it's all about, you might want to check the interview on AFS I did with Emmanuel Dreyfus on DaemonNews, as mention in this blog post.
More details about the sarna.org AFS cell:
The Kerberos 5 server is a dedicated Soekris 4801 running NetBSD only the Heimdal KDC software and NTP service for my network.
NetBSD server on Intel EM64T hardware (currently running NetBSD/i386, though I plan to upgrade to NetBSD/amd64 at some point) with 1TB hardware RAID 5 storage divided into several ~200G partitions plus a small root partition. Currently only one partition is used for AFS volumes, and a second is used for online backup of about 30 days of all AFS volumes (currently, there is extra space so more is being kept online). As I need more space (I am centralizing media files, photos, and other items in my AFS space), near-line backup will be moved to external USB drives.
Volume backups older than 30 days are burned to DVD as there are enough files to fill discs. Current backup policy for all volumes is a full dump every month and nightly differential backups relative to the last full dump (so I can restore point-in-time with at most two backup files). As I get more media-heavy, I will likely develop different backup policies that apply to those, as they rarely change.
Besides AFS volumes, plain partitions (root partitions, etc) on several other systems are also dumped into this dump pool for eventual DVD archiving on a similar full-monthly/level 1 nightly system. The KDC's filesystem is dumped in encrypted form using PGP. The private key is kept offline.
I use OpenAFS for the server software, and two different clients: OpenAFS on Windows, and Arla on NetBSD and Mac OS X.