Just to thin you out a bit and speed you up...
The issue that he's referring to is that you can not access a Stateful Session Bean by more than one thread concurrently. This is an specified limitation within the EJB spec, so it's not (directly) related to what you're referring to.
In a web environment, this is rarely an issue (at least historically) because you rarely had more than one thread acessing a Stateful Bean for the same client (i.e. the same bean) simultaneously. Now, today, with all of the Ajax hulubaloo, I can see this issue cropping up more and more.
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