This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
It is definitely not recommended way of using session beans. Two or more clients invoke business method on the same instance of EJBObject simultaneously can be done via user developed multi-threaded program, which is a strict no-no in EJBs. The obvious problem areas would be transaction, security management.