Disclaimer: I was one of the technical editors of this book, so I may be biased.
While I haven’t received the book in its final form yet, I’ve read all of it, and I can say that the author does a good job at introducing inexperienced programmers to web development with Ruby and MongoDB.
This is a hands-on book and you’ll get most out of it by following all the exercises and doing them on your own. From getting all the necessary components and installing them, to developing apps with Sinatra and Rails, a lot of ground is covered.
While the author does tackle some more advanced topics, they are clearly not the focus of this book (it’s subtitled “Beginner’s Guide” for a reason) which will leave more experienced developers wanting for more. However, the presented material is well written, chapters build on each other and if you are new to web development with Ruby/RoR and/or MongoDB, this is a good title to get you up to speed in just 300 pages.
If you are a more experienced Ruby developer or are already very familiar with MongoDB, this is probably not the book for you, even though you’ll probably still get something out of it.