The next version of the framework will be more focused on dynamic languages and will keep the C# and VB.NET in parallel.
It also introduces extensions to support the parallelism in a declarative and imperative way. In that extensions, we will have PLINQ (for Parallel LINQ) to parallelize LINQ queries, TPL (Task Parallel Library) and CDS (Coordination Data Structure).
One of the new feature is the ability to install the client profile on every configuration whereas for the previous versions, it needed to be installed on a clean infrastructure.
Among other things, new controls for WPF, multitouh support under Windows 7 and an easyness to develop user interface based on datasource even though the Entity Framework is not yet supported in the presented version. The MVC will be implemented with a dynamic data support.
On the WCF side, some enhancements have been implemented such as SOAP over UDP and more WS-* support. Moreover, building a RESTfull application will be simplified.
With the .NET framework 4, WF and WCF will work together as they will be completely integrated. Nevertheless, and big change, workflows will be defined in XAML-only by default. On the other side, more activities will be available in the toolbox.
A lot of improvements in terms of performance and scalability have been done and and a new workflow type is now available : FlowChart. Now, activities can receive arguments and return values.
When developing custom activities, it will be possible to define a custom design using a WPF designed
Basically, and in short, the 4th version of .NET allows a workflow (WF) to be exposed using WCF (interface), while, on the hosting side, it will rely on Dublin which is a Windows Server 2008 Application Role extension.