I've enjoyed Ars Technica for a long time, even from the pre-history before RSS when you had to remember what sites you liked to visit. Having an interest in computer architecture, I thus grabbed (a signed copy of) Jon Stokes' Inside the Machine quickly when it came out.
Having learnt what I know about architecture the "traditional" way (e.g. textbooks and courses) I was interested in the "beginners guide" approach. The early parts of the book, explaining the basics of microprocessors, rely quite heavily on analogies (the "file clerk", the "document storage room", the "SUV factory" etc). Personally, I'm not sure how much this aids the understanding of the material — for mine the length of time spent describing the analogies gets in the way of the material. I understand, however, that I am not the target market for the early part of the book. The introduction to instruction encoding with the "DLW" architecture serves as a good illustration; it is the type of stuff I think should be in every introductory CS course. The diagrams throughout are very clear, and it really lives up to its billing as an "illustrated guide".
For mine, what is most impressive is the later chapters, which are an unrivalled review of x86 and PowerPC architecture. They are clearly well researched, and step you through the architecture and its history logically and clearly. The level of detail is perfect, giving you more than enough depth to understand what is happening but not bothering to delve into irrelevant esoteric implementation details which would simply make the book fatter (c.f. H&P). If you've studied architecture before you can skip to Chapter 5 and dive into this bit straight away.
If you have more than a passing interest, I still think investing in a copy of Hennessy and Patterson and plowing through the first few chapters (and appendixes) is an unrivalled introduction. But this book is about 1/3rd as thick, much easier reading and, more importantly, is the only current compendium on modern (i.e. still in production/development) architectures. I shudder to think how long was spent pouring over architecture manuals, whitepapers and old HOTCHIPS papers to distill the useful information it contains. Computer architecture is a fascinating art, and this book may well be the best passport to the otherwise inaccessible city of transistors just below your fingertips.