Guillaume pointed out recently on the hibernate-dev mailing list that is has been a very long time since the last release of Hibernate JPA Metamodel Generator release and that it is time to do another one. And we listened. We just released 1.3.0.Final. As usual, you can get the artefacts from the JBoss Maven repo or from SourceForge.
Don't say that we are not listening to our users and contributors. There might have been, however, some self interest in Guillaume's request. After all he reported three of the 10 resolved issues and even contributed patches to fix them. Thanks for your help! To single out one of the 10 issues, it should be METAGEN-92. Its fix will make sure that the annotation processor will now also work with JPA 2.1 configuration files (persistence.xml and orm.xml).
In case you forgot how to setup the annotation processor in Maven have a look at this post and don't forget to report any issues in the Hibernate JIRA project METAGEN.