If you are considering using XML in SQL Server 2005, this book will pay for itself quickly. The clear examples of creating XML Schema collections, altering them, etc. are very helpful.
The only problem with this book is that SQL Server 2005 does not fully support XML Schemas. Because this book was written using a beta product (I believe) perhaps the author could not have know exactly how the final version would shake out. However, partial support of standards is important to any developer. You often find out only by trial and error what is supported and what isn't. The Wrox web site offers nothing of the kind for this book. So buy this book, but be aware if you are using complex XML Schemas there may be some surprises (e.g., notation not supported).