The basic concept of EJB remains same. Its only the working of EJB has been changed 3.0. The HFS is still a good book of getting the basics of EJB right. I mean conceps like what is EJB, Session Bean, etc etc. The entity bean section is also worth reading as EJB 3.0 does not modify the design of entity bean.
Note that EJB Entities is different from Entity Bean. Entities is based on JPA (Java Persistence API).