I just finished Andy Clarke's Transcending CSS and deciding to delve into The Elements of User Experience which I picked up because, skimming, I realized it was giving me names for what most of us are already doing.
So far, it's concise and Garrett does a nice job of making sure that a web developer doesn't leave a reading of the book with impression that user-centered design isn't connected to a much bigger discipline, human factors design. Garrett hasn't used that word -- or Computer Human Interaction -- but he's careful to situation user-centered, user experience design into a broader context, where engineers and other subject matter experts have been working on design for the way people use things like alarm clocks and gas grills.
One thing I found most intriguing from my initial skim at the bookstore, was that I (and a lot of us) have been doing "information architecture" and "information design" -- but we didn't necessarily call it that. We've been doing user interaction and user experience, too, we just haven't called it that. If you've been developing Web sites with the user experience in mind, if only because you are also a heavy user of the Intertoobz, then much of what is discussed in thiis book is intuitive -- what you already do.
That may not be the case for people who've been more focused on programming or who get a charge out of building the technology and would, perhaps, love it if they had advanced users for whom there was no need to write meaningful error messages -- let alone test and test again until you break the code, accounting for edgecases, not just the tech savvy user.
For me, probably because I always had to stick around for the consequences of what I built when I was doing elearning, the name of the game has been user-centric development and design practices. When good training via elearning means the difference between following government regulations about security and privacy -- and not doing so -- it mattered a great deal whether the Learning Management System was usable. Moreover, in elearning, people who focusing on user experience early on -- because the user's environment mattered to whether or not they learned anything.
In that sense, much of what was presented in this book was mostly key terminology that is only recently become shared terminology in the wider UI/UX community. As another reviewer mentions below, the best part of the book are the schematics depicting the elements of the user centered design and the relationships between these elements. The book is a handy reference to keep at your desk and to recommend to developers who haven't developed in user-centric environments, or to a colleague who would like to broaden her understanding of UI development in this wider context, particularly as it relates to project management and the software development lifecycle.