Now that Java EE 5 is nearly baked, I am looking for pointers to "Best Practices" for extending existing J2EE 1.4 applications into Java EE 5 environments.

For example: if I have a J2EE 1.4 ejb-jar and I want to start doing EJB 3.0, what should I do?

a. change the namespace in my existing jar, then rock and roll...
b. create a new jar for my EJB 3.0 components and "call" back and forth between the two jars...

I would imagine that we don't get to mix-and-match @Entity and CMPs...

Are there other "gotchas" out there?