Overall, I found this book to be well organized and very readable.  In fact, it is one of the most readable technical books I have ever read.  ASP.NET Web Parts are an exciting and powerful technology and it takes a well written and technically complete book such as this one to unlock the hidden secrets for you.  This is not a book for the true beginner, however.  You should be familiar with the concepts behind n-tier applications and interfaces, since the sample application uses both.  A background on these is outside the scope of the book and the author makes no attempt to define them (examples and definitions abound on the Internet).  The examples in the book use Visual Studio 2005, and although you could use Visual Web Developer Express for these examples, some of the screens would look different.

In addition to the print version, the publisher offers a PDF version from its website.  Chapters 2 and 9 are available from the publisher's website as well, so you can literally try before you buy.  The purchase of the book allows you access to online forums on the publisher's site as well.