I know of a few GlusterFS installments being used in production. You may want to look at some of the Scalable Informatics products if you want a commercially supported system.
The GlusterFS team also had a booth at Supercomputing 09 where they demoed their systems. I think it’s by no means a “mature” technology, but it’s certainly usable in production in its current state. Note that by their very nature clustered filesystems are finicky to set up and maintain.
As far as Ceph goes, I’ve never heard of anyone using it for anything other than testing. It itself is based on a regular filesystem that hasn’t even reached maturity yet (Btrfs). I wouldn’t use it for anything other than a plaything at this point.