The counterpart to the EJB 3.1 spec, the Java Persistence API 2.0 spec has just published a first public draft at JSR 317.
There have been so many changes to the spec since JPA 1.0 (JSR 220) that I don't want to mention them here.
Mike Keith has recently written an article that describes some of them.
Like in JPA 1.0, JBoss has contributed a lot to the stuff. Both Gavin King and Emmanuel Bernard were very active in this update.
But check them out by yourself at the JSR 317 spec page.