With GWT, when exactly do you need DTOs for your entities ?

Hi,
I need some clarification regarding the use of JPA entities within a GWT application.
I have always read that you need to create a DTO for each entity that you develop in a GWT application because of some serialization problem.

But if you look at this skeleton for a GWT-JPA application, you will notice that there are no DTOs !
http://code.google.com/p/gwt-hardwarestore/

So i am not sure what's really needed.
Are DTOs really needed ?
My GWT application uses the MVP Places and Activities pattern.

Thanks for helping.

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