I mean If I was using WCF over http I wouldn't hesitate.
My ORM is LLBLGen Pro which provides me with some pretty nice entity collections features, like tracking changes and other. If I would go the DTO path I would lost this functionality. For now there is on the client side a Web app, which does not need any tracking changes funcionality, but maybe some day there will be a silverlight app on the client side.
What do you guys think on this ?
Even when your transport binding is named pipes, WCF will still serialize and deserialize the messages. This means that your objects will be copied going back and forth.
Even if you share the type between client and service (not generally recommended) you will still have copies going back and forth. Essentially, even without explict DTO types, your objects will still be treated as implicit DTOs.
Oh, and it will only work if they are already DataContracts or IXmlSerializable.