The mediastore demo included with the GAE sdk does not work (I placed my war here: http://vanbrabant.eu/mediastore.war).
I tested it with the precompiled beta2 and with HEAD from github against JBoss 7.2 Final prerelease.
When I open the mediastore app in my browser it keeps waiting for a result. The jboss logs show the persistence being enabled and there it stops. It can only be stopped by a kill -9.