Hi Amit-
Actually, if you are using annotations with EJB 3.0 (note that you can use either annotations or ejb-jar.xml) the things you mention *would* change.
* Transactions
If you prefer annotations (and many people do), you could specify transaction attributes for the bean, or for any specific method, using the @TransactionAttribute annotation.
* Exceptions
In EJB 3.0, you no longer need to throw java.rmi.RemoteException from methods declared on your remote interface.
*Security
Security roles and method permissions also may be specified using annotations.
The main thing that *doesn't* change is the actual business logic in your business methods. If you accept the default transaction and security settings for your session bean, all you are left with to code is a simple class that is annotated @Stateless or @Stateful and contains ordinary methods for your business logic.
Looking beyond the defaults goes beyond the scope of this reply, but there is much written on the topic.
Regards,
Jon
http://www.amazon.com/Beginning-EJB-Application-Development-Professional/dp/1590596714/sr=11-1/qid=1162493716/ref=sr_11_1/002-0255731-2231223