Andrew Zhu works for Microsoft in Shanghai and has been using WF4 since the very early days. He frequently answers questions on our internal mailing list and on the WF Forums so when I heard that he was writing a book about WF4 I knew it would be a good one.
I just got my electronic copy and I have to say it looks great. Of course it covers the basics but also gets into great detail especially in the chapter on rehosting the WF designer, it’s definitely on my recommended list.
Check it out – Windows Workflow Foundation 4 Cookbook