My latest WCF/WF article was recently published in the January issue of MSDN Magazine. It focuses on the new features found in WCF/WF 4.0 with a special focus on the changes to the WF programming model, XAML-based declarative workflows/services, and the new hosting environment provided by the new "Dublin" application server extensions. .NET 4.0 marks a big shift for WCF/WF moving forward. Check it out here.
