What are the special design care that must be taken when you work with local interfaces?

It is important to understand that the calling semantics of local interfaces are different from those of remote interfaces.
For example, remote interfaces pass parameters using call-by-value semantics, while local interfaces use call-by-reference.
This means that in order to use local interfaces safely, application developers need to carefully consider potential deployment scenarios up front, then decide which interfaces can be local and which remote, and finally, develop the application code with these choices in mind.
While EJB 2.0 local interfaces are extremely useful in some situations, the long-term costs of these choices, especially when changing requirements and component reuse are taken into account, need to be factored into the design decision.