I think requests for book reviews are uncommon on other stack exchange sites because there are far too many books and it's not even sure there are other StackExchange users who have read some book I might be interested in.
But there aren't that many Mathematica books, and it isn't unreasonable that at least popular ones have been read by a few Mathematica@StackExchange users.
EDIT 2: I think there has been some confusion about this question. I'm not asking about book recommendations (which is just asking for an infinite list) but about reviews for a specific book.
For example, a "book review" question could look like this:
I've seen the book Front-End Vision and Multi-Scale Image Analysis: Multi-scale Computer Vision Theory and Applications, written in Mathematica on Amazon. Has anybody read the book? Would you recommend it? I'd like to use Mathematica 8.
The book costs $149 and has no reviews on Amazon.com, so I think this might be quite interesting to potential buyers. An answer could look like this:
I found this book very useful, because it has an almost unique focus on scale-space based image processing. Using Mathematica for this book makes a lot of sense, because many of the results are derived from first principles using calculus, then applied to image processing using transformation rules. The material you will find in this book has almost no overlap with standard image processing textbooks. On the other hand, if you want an introductory text into standard image processing techniques, you should get another book.
Unfortunately, the book is written for Mathematica 4, so it makes no use of Mathematica's new image processing functionality. It uses 2D arrays to represent images and
DensityPlotto display them, so if you're looking for an introduction into Mathematica's image processing functions, this is again not the book for you. But if you're already comfortable with the new image processing and graphics functionality, you will have no problems translating the samples in the book.