TL;DR: It is a good book.
I won the Agile Testing book in lottery while I was at The Austin Workshop on Test Automation (AWTA) in Austin, Texas, in January 2009. I have met both authors, Lisa Crispin and Janet Gregory, at AWTA and even recorded a podcast about the book. I was planning to read it since then. But, as it usually goes, I had other things to do. I finally decided I will read the book a few months ago, and I was reading it a few pages a day. While reading it, I had to quickly read another book, so everything is a bit blurry. A few days ago, I have finally read the book.
Probably the most useful part of the book for me was part 3, the agile testing quadrants. It was introduced by Brian Marick way back in 2003, but I do not think I have heard a lot about it until I found it in the book.
I am pretty bad at book reviews, so I will not go into details. There are a lot of reviews at Amazon, if you like to read them.