Shared data object between WCF service and Silverlight app

There is a good example of how to do this here by Pete Brown. Using that approach you can use the same classes in both the Silverlight client and in the WCF service without having to use the generated objects.

Declare the data entities in the WCF service or a project that the service refereneces, then from the Silverlight project add the entities as links and make sure the "Reuse types in referenced assemblies" checkbox is selected from the Service Reference Settings dialog.

You can put the types in either the Silverlight or WCF side.

I have tried doing things this way and found that using DTOs instead and mapping them to the entities in the Silverlight side to be much cleaner and easier to work with although I did write a bunch of mapping code to get the DTOs into the entities and vice versa.