one more thing:
when do I have to specify a @Local and a @Remote interface? Is @Remote usefull in seam context anyways? As I understand it seam can use objects even without these interfaces.
You only have to use @Remote when you plan to make the session bean available to clients outside the container JVM (for a client application).
There are a number of advantages to using EJB3 session beans instead of POJOs.
SFSB replication across the cluster is handled by the container, as is persistence context injection and transaction demarcation.
As I recall, the Seam documentation says that SFSB replication across the cluster is more efficient than that of Seam POJO components.