Serge Luca has created a walkthrough on "Exposing a Workflow as a WCF Service in Visual Studio 2008 beta 1". In this post he guides the reader step-by-step through the new Send and Receive activities in Visual Studio 2008 beta 1 (formerly "Orcas") and in the .Net Framework 3.5. From creating the service contract, adding a workflow component, hosting the service and finally consuming it from a client application; all steps are illustrated with screen shots.
This is basically a summary of a session Serge delivered for Microsoft Belux. The article can be considered as an update to this article.