Its exciting to see the real implementations released in February 2006 for EJB3 persistence layer. Development with WebLogic 9 and EJB3 looks very promising.
Definitely hibernate and ejb2.1 came much before. Most of the j2ee ecommerce/ products and frameworks based on portal,rule engines, content and workflow solutions still use ejb2.1. EJB3 is still considered as a discussion point for technical architecture. While JBOSS already has EJB3 preview release last year, IBM Websphere v6 onwards may release EJB3 container soon so that developers can develop components with IBM Rational Application developer.

Its exciting to avoid creation of home and remote interfaces with EJB3 code. EntityManager does everything and sets a great persistence development principle based on JSR220. Writing POJOS in EJB3 is quiet tricky. But you can write them. Tools help for annotations (embedding details in code) So not to spend too much time on maintainability issues. I am sure other peristence engines like Toplink will also support it more.Hibernate components and entity beans would definitely defer since their life cycle is different. When EntityManager and ejb3-persistence with JDK1.5 is around, its exciting to use jdk1.5 features in development and make use of EntityManager when you dont have home interfaces. I may write more comments in detail.

Good Luck
Maneesh Innani
Senior Technical Architect