I don't know, really. I've not bothered with EJB3.0 entities. I tend to do my own persistence with JDBC, sometimes using the Spring Framework to avoid loads of boilerplate JDBC code. I've mucked around with Hibernate too, which by all accounts is similar to how EJB3.0 Entities work.
Having been involved with a non-trivial project using EJB2 I'm pretty anti-EJB anyway.
Tim