It gives a great introduction to all Amazon Web Services (AWS), not just what they're good for but also hands on how to use them (mostly through command line commands). The book also focuses on several real world products by the authors and how they use AWS. It even goes into what spikes and "Internet scale" popularity could do to your application and how to manage it. For me it was a great read, but it doesn't have focus on the EC2 service as the title implies as it goes through most services on equal amount. If you just want an introduction you can probably just browse around the AWS website.
Conclusion: Read it if you want to learn more about AWS, not if you want hardcore EC2.