Mr. Glowacki,
Sorry for the late reply to this...I just came back from vacation.
Porting from
EJB 2.1 to EJB 3.0 is quite smooth because EJB 3.0 containers are 100% backwards compatible. For further coverage, please check out the migration chapter in EJB 3 in Action. We talk about these issues in fairly good detail.
Hope it helps,
Reza