This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
There is only a difference if you use local interfaces according to EJB2.0. With local interfaces parameter (VO) are passed by reference. In the other case (remote interfaces) parameters are passed by value (they are copied) and serialized due to RMI.