I've been interested in mongodb for quite some time now, so when a co-worker of mine asked if I was interested in reviewing a book about mongodb, I of course said yes! She put me in touch with the publisher of a book on MongoDB and web development entitled, "PHP and MongoDB Web Development". I was given a electronic copy of the book to review, and so here are my thoughts after spending a few weeks reading it and playing around with mongodb independently.
This book is subtitled "Beginner's Guide", and I think it achieves its goal of being a good introduction to mongodb for beginners. That being said, my primary criticism of the book is that it should include more information on some more advanced features like sharding and replica sets. It's easy to create web applications for small scales, or that don't need to be up 99.99% of the time. It's much harder to design applications that are robust to bursts in load, and to various kinds of network or hardware failures. Without much discussion on these points, it's hard to form an opinion on whether mongodb would be a suitable choice for developing large scale web applications given the information in this book alone.
Other than that, I quite enjoyed the book and found it filled in quite a few gaps in my (limited) knowledge. Seeing full examples of working code on more complex topics like map reduce, GridFS and geospacial indexing is very helpful to understanding how these features of mongodb could be used in a real application. I found the examples to be a bit verbose at times, although that's more a fault of PHP than of the book I think, and the formatting in the examples was inconsistent at times. Fortunately all the examples can be downloaded from the publisher's web site, http://www.packtpub.com/support saving you from having to type it all in!
The book also covers topics like integrating applications with traditional RDBMS like MySQL, and offers some practical examples of how mongodb could be used to augment an application which already is using SQL. It also includes helpful real world examples of how mongodb is used for web analytics, or by foursquare for 2d geospacial indexing.
In summary, the book is a good introduction to mongodb, especially if you're familiar with php. If you're looking for more in-depth information about optimizing your queries, or scaling mongodb, or if your language of choice isn't php, this probably isn't a good book for you.