This is the same question that was asked here, but it's been almost two years since.
Meanwhile Ceph has seen constant development (361 kernel commits) and btrfs, in my opinion, is on the verge of production readiness. Both projects' web sites have (dated) sections that clearly state otherwise, though.
Gluster not being inactive either has since managed to put out releases 3.1, 3.2 and is about to release version 3.3. Along the way they were acquired by Red Hat, which probably contributes to steady development for the mid distant future.
So, has Ceph gained any production level deployments yet? How does it compare to GlusterFS nowadays?