I had a client running PHP from a gluster storage, split across two nodes. Performance was horrific, although some of the sites were improved via Varnish we eventually had to move to local copies of files & rsync. Not pleasant.

Gluster is nice, but you have to accept the fact that it is slow, and upgrades are painful. (We had issues where clients and servers had to be updated at the same time, to avoid interoperability issues.)