Years ago, we had a NetApp filer, and its daily snapshots were easy to use and were worth their weight in gold when you had the occasional software disaster (e.g., Netscape once crashed on me, leaving behind garbage in its config files). Just cd yesterday and copy the files back to today. The Infrant box, built on Linux and using its snapshot feature, gets part way there, but it's not nearly as easy to get to the snapshots. ZFS, if it lives up to its marketing, lets you make a snapshot any time you want with very low overhead and a simple naming convention that seems suspiciously like the way NetApp does it. ZFS's RAID support and end-to-end integrity checks are also very impressive. ZFS's send and receive features appear to make it almost painless to synchronize your filesystem with a remote server.

All very impressive stuff, but it's a valid question to ask what degree of tools support you'll get standing behind it if/when something goes wrong.