If I would build a big WCF RIA Services application with multiple domain services how could I have certain entities, which are shared between those domain services and exposed by them in different context. For example I could have a Cutomer entity, which is exposed both by Orders and Loyalty modules/domain services. At least my own experiments with [ExternalAttribute] and others seem to indicate that this is not supported by the framework very well.
Have you seen this tutorial by Microsoft?
http://msdn.microsoft.com/en-us/library/ff422034(VS.91).aspx