Being first to support a developing specification often means that inconsistencies will crop-up between the implementation and the official specification. Since the authors have been involved with OpenSocial since the beginning, they provide numerous stories about how the specification developed, and how it's roots led to certain design decisions. At the time of writing, the specification is 0.9 as well, the book is specifically about creating applications that run on MySpace, so there are a number of quirks between the official specification and MySpace's implementation. While these don't seem to be major, they need to be observed and the writers do a good job of explaining the quirks and how to handle them. With that in mind, Building OpenSocial Apps takes readers right from the first MySpace "Hello World" into full applications.
The book starts off with creating the traditional "Hello World" application before moving into more advanced topics. Essentially the book is broken down into three sections: building an application on MySpace's servers, creating apps that run off other servers (necessary for larger applications) and dealing with growth and security. Throughout the book, the readers work with a simple Tic-Tac-Toe game (is there any other kind?) that can be downloaded and is used as a starting point for learning about the MySpace Developer Platform and OpenSocial.