Kent Beck is a wonderful writer and has many good points to make in this book, but I can't recommend spending money on it unless the publisher produces a new edition correcting its hundreds of errors. Pages appear in the wrong order, parts of paragraphs are randomly duplicated, code samples are formatted incorrectly and nearly unreadable, and words appear in the wrong typeface making it difficult to distinguish identifiers from prose. Many of the articles appear to have been scanned in using OCR software and not subsequently proofread, or possibly proofread by someone who didn't understand the content. The lack of quality control is simply appalling.
Better organization of the material would also have been helpful. The "Sorted Collection" is sorted by date only. This may be useful to those interested in tracing the recent history of Smalltalk, but not to those wanting to learn most efficiently.
Much of the material in this book is better and more thoroughly presented in Beck's other books. At best, this book can be seen as a haphazard introduction to Beck's ideas that will spur some programmers to learn more about Smalltalk, object-oriented design and Extreme Programming.