I read Jeff Barr's book on Amazon Web Services (Kindle edition) - using a Droid phone and a Kindle device. My take thus far: this is a great resource for getting a grip on the fundamentals of Amazon Web Services. I worked extensively with some AWS services (S3, SimpleDB, and EC2) and applications like SDB Explorer and Bolso prior to reading the book, but I can still say that I've learned quite a bit from this book.
The code for the programming examples is in PHP. Making the examples work on your system requires creativity at some points. The author states his technical expectations early in the book and it's expected that the reader has a base proficiency with PHP, along with some system administrator skills. I found it fastest to download and use the CloudFusion code on GitHub; I'm running the examples on a Fedora 8 EC2 instance.
Barr uses the "programmable data center" concept to explain cloud computing, and when you get to chapter 5 and run the EC2 API example in PHP, it's an empowering feeling. At that point, theory and practice come together. This script ran successfully (launching an EC2 instance, claming and mapping an IP, then creating and attaching EBS volumes programatically) the first time I ran it. Likewise, the modular application (using SQS) that scrapes web site images and creates composite pages gave me a sense of AWS' potential.
I have to say that I hit a wall just beyond the halfway point in this book, when it came to getting the AWS CloudWatch code functioning. At this point, to move forward with this section (CloudWatch, EBL...), I feel that I'll have to learn more about the CloudWatch API. In this case, I feel that the book and code sample explanations for working with the CloudWatch API are insufficient. (I got the command line tools for CloudWatch running, but not the PHP code example, particularly listing measures. Couldn't fix it by googling or reading on the AWS PHP SDK documentation.) In short, I had to skip most of the chapter and just go on.
There are chapters covering SimpleDB and the RDS (Relational Database Service). For SimpleDB: I found myself using the book examples as a launching point for building my own small SimpleDB applications. You can take Barr's code examples and the SimpleDB API documentation at URL http://docs.amazonwebservices.com/AmazonSimpleDB/2007-11-07/DeveloperGuide/ (API Reference/Operations) to programatically work with SimpleDB as needed for your project. That is, you can use the object-oriented code examples and the Request and Response information to create the needed applications - which illustrates the programmable data center concept better than anything.
Overall, highly recommended. I found some challenges in working with the Kindle edition, in terms of viewing illustrations. I found it possible to run most, but not all, of the code examples in the book. And I'm much more proficient with and knowledgeable about AWS than when I started readng it.