The in's and out's of XML are covered in the first 4 chapters, providing some helpful XML reference material. I found the chapters on Datasets and using XSLT with ASP.NET most helpful. Explanations on quick ways to accomplish actions (for instance writing out a dataset to an xml file) are coupled with Dan's take on the BEST way to do these tasks.

Also, the book chapters are logically put together to allow you to pick and choose chapters when you need them as a reference. A good technical read as well. Right now this is my first reference for using XML with ASP.NET.