I want to talk about EJB3 more later when I have a bit more time. If you want to get a taste for EJB3, I suggest looking at the EJB3 TrailBlazer. It will give you a taste of EJB3 development.
I've recently completed a non-trivial application using EJB3, and I have to say that EJB3 is extremely cool. I would absolutely consider EJB3 as my first choice for doing J2EE application development.
What does JBoss ADD to EJB3? That's interesting. We add JBoss AOP and our annotations library, giving you additional aspects you can easily apply to beans. Very cool. We also add Hibernate, which is our persistence implementation. You can customize the persistence of EJB3 entity beans by using any of the hibernate configuration options you want. So, you get really advanced mapping options. You also have the second level cache options with hibernate for caching. I've been playing with JBoss Cache as the second level cache.
For EJB2 migration, you do need to rewrite some. The good news is that you can mix and match EJB2 and EJB3 in an application, so you can take your migration one step at a time. Based on my experience so far, it is well worth the effort to migrate. EJB3 is great.