My series of four digitial articles have been published by Addison-Wesley. You can get the links to purchase them and the associated source code from my web site.
I have tried to explain, in practical terms, what you need to know to actually build real world software using Windows Workflow. There is a tiny amount of theory to explain the underpinnings. The vast majority of the explanation uses code examples to illustrate all the key points. The last shortcut in the series has two extended examples that illustrate how to build custom activities.