I borrowed a copy of a new workflow book ""Programming Windows Workflow Foundation", sub-titled "Practical WF Techniques and Examples using XAML and C#", by K. Scott Allen. It's not a big book  - a little over 220 pages. It's very readable, and provides a high level overview of the key areas of interest in Windows Workflow Foundation, interespersed with short code extracts and screen dumps. If you are new to Workflow and want to get to grips with it, and gain a rounded knowledge of the subject matter (which is not always a trvial matter), then this is a great starting point.