"We hope to have the system usable (for non-critical applications) by the end of 2009 in a single-mds configuration. Even then, however, we would not recommend going without backups for any important data, or deploying in situations where availability is critical."
It looks interesting, but not ready for prime time. Anyone using this in the wild?
In fact, Ceph is practically what you'd call "stable" at this point (which is not to say it's "production-ready"!), and we've actually begun testing it as a backup/replacement for our poor backup.dreamhost.com server (who's been having a terrible time for months)!
If YOU would like to give Ceph a try, please, download away... it's free!
Also, we're going to be setting up a "playground" test-bed where anybody can try out a Ceph installation we set up and maintain in our data center. If you're interested, just email beta@ceph.newdream.net, and we'll send you an invitation when it's ready!
[edit: added the bit about beta testing]