By default, JEE synchronizes access to a stateful EJB to only allow a single thread at any given time.
EJB 3.1 brought about the @Singleton annotation, along with two simple annotations: @Lock(READ) and @Lock(Write). These two anntotations should be ported to Stateful EJBs. Since the whole world is going concurrent, these controls will be completely necessary in the future. This would be extremely useful in Domain Driven Design.
The usefulness of this suggestion is greatly enhanced if there was a way to grab a handle to a Stateful EJB3. I'm putting the latter suggestion in another JIRA ticket.