This book is not for people who want to know "What .NET My Services" is, its a developers companion with about three quarters of the book being code and syntax.
This book is currently only of any use to you if you are on the .NET My Services Alpha program...
The book is the Microsoft .NET My Services Developers Dictionary, with a chapter devoted to the "what", "when" and "why" of the subject and the rest devoted to "how".
I would not recommend this book to anyone who wants a background as to what this is, but only those who want to start coding with .NET My Services.