What's New in Orcas

The official list is a little hard to find but here's the overview of the big new WCF features in Orcas.

• WCF and WF Integration-Workflow Services: The .NET Framework 3.5 unifies the Windows Workflow Foundation (WF) and Windows Communication Foundation (WCF) frameworks so that you can use WF as a way to author WCF services or expose your existing WF workflow as a service. This enables you to create services that can be persisted, can easily transfer data in and out of a workflow, and can enforce application-level protocols. For more information, see Creating Workflow Services and Durable Services. For code samples, see Workflow Services Samples.
• Durable Services: The .NET Framework 3.5 also introduces support for WCF services that use the WF persistence model to persist the state information of the service. These durable services persist their state information on the application layer, so that if a session is torn down and re-created later, the state information for that service can be reloaded from the persistence store. For more information, see Creating Workflow Services and Durable Services. For a code sample, see Durable Service Sample.
• WCF Web Programming Model: The WCF Web Programming Model enables developers to build Web-style services with WCF. The Web Programming Model includes rich URI processing capability, support for all HTTP verbs including GET, and a simple programming model for working with a wide variety of message formats (including XML, JSON, and opaque binary streams). For more information, see Web Programming Model. For code samples, see Web Programming Model Samples.
• WCF Syndication: WCF now includes a strongly typed object model for processing syndication feeds, including both the Atom 1.0 and RSS 2.0 formats. For more information, see WCF Syndication. For code samples, see Syndication Samples.
• WCF and Partial Trust: In .NET Framework 3.5, applications running with reduced permissions can use a limited subset of WCF features. Server applications running with ASP.NET Medium Trust permissions can use the WCF Service Model to create basic HTTP services. Client applications running with Internet Zone permissions (such as XAML Browser Applications or unsigned applications deployed with ClickOnce) can use the WCF proxies to consume HTTP services. In addition, the WCF Web Programming Model features (including AJAX and Syndication) are available for use by partially trusted applications. For more information, see Partial Trust. For code samples, see Partial Trust WCF Samples.
• WCF and ASP.NET AJAX Integration: The integration of WCF with the Asynchronous JavaScript and XML (AJAX) capabilities in ASP.NET provides an end-to-end programming model for building Web applications that can use WCF services. In AJAX-style Web applications, the client (for example, the browser in a Web application) exchanges small amounts of data with the server by using asynchronous requests. Integration with AJAX features in ASP.NET provides an easy way to build WCF Web services that are accessible by using client JavaScript in the browser. For more information, see AJAX Integration and JSON Support. For code samples, see AJAX Samples.
• Web Services Interoperability: In the .NET Framework 3.5, Microsoft maintains its commitment to interoperability and public standards and introduces support for the new secure, reliable, and transacted Web services standards: Web Services Reliable Messaging v1.1, Web Services Reliable Messaging Policy Assertion v1.1, WS-SecureConversation v1.3, WS-Trust v1.3, WS-SecurityPolicy v1.2, Web Services Atomic Transaction (WS-AtomicTransaction) Version 1.1, Web Services Coordination (WS-Coordination) Version 1.1, Web Services Policy 1.5 - Framework, and Web Services Policy 1.5 - Attachment. Implementation of these protocols is made available using the new standard bindings, <ws2007HttpBinding> and <ws2007FederationHttpBinding>, which are documented in the Web Services Protocols Interoperability Guide. For a code sample, see WS Binding Samples.