why do you need 2 assemblies? client/server?
If so then you can use pocos/dtos on the client and keep the domain entities on the server (adapter or SS will for for this scenario) the server would need to map the pocos to entities.
If you want the entities on both the client and server, then you must use adapter.
If your designing a thick client or web app I would keep the code in one inclusive assembly and abstract the layers logically by objects, not physically by assemblies.