A very good tutorial/article about WF4 (not so many out there these days).
A Developer’s Introduction to Windows Workflow Foundation (WF) in .NET 4.
TOC
Overview
What’s New in WF4
Designers
Data Flow
Flowchart
Programming Model
Windows Communication Foundation (WCF) Integration
Getting Started with Workflow
Workflow Structure
Workflow Templates and the Workflow Designer
Data flow in workflows
Variables – storing data
Arguments – passing data
Expressions – acting on data
Building your first workflow
Tour of the workflow activity palette
Activity Primitives and Collection Activities
Control flow activities
Migration
Flowchart
Messaging Activities
Transactions and Error Handling
Creating and executing workflows
Options for designing workflows
Options for executing workflows
Workflow Extensions
Persistence
Tracking
Creating custom activities
Activity class hierarchy
Composing activities using Activity designer
Writing custom Activity classes
Additional activity concepts
Activity designers
Rehosting the workflow designer
Workflow Services
Conclusion
About the Author
Additional Resources