Software developers like being "agile", whatever this means. They say being "agile" liberates their creativity and lets positive energies of the Universe flow through them to the code to (hopefully) solve customer's problems. They are committed to using all the practices that e.g. XP suggests, but it generally would be better if somebody else writes unit tests. For me definition of "agile" changed forever when I first watched David Anderson's interview "Writing Agile Software" and read his book Agile Management for Software Engineering. All the other books on "agile" topics I've come across focus of how freaking cool it is to use agile to develop software, of course, from the point of view of developers. And you are a, hm-m-m, short-sighted conservator if you want developers to do development with, say, RUP.
"Agile" does not equal to "Say no to BDUF and documents". David in his book explains what is agile and why it is better for clients and their businesses.
Jurgen Apello in his blog provides a review for this book, but focuses mostly on the form, not the meaning. True, the book is not fun and makes you think, but it is gratifying when you finally get the clue. Again, this book is not about the fun you get working on agile project, it is about why agile works in business landscape.
Anyway, if you want to better understand the book, my suggestion is to watch the video first.