I just got a copy of this and had a good read through it. In summary, it is a good introduction to the RSS technologies that I'd recommend if people are looking to get up-to-speed with RSS.
A substantial part of the book is on RDF, RSS 1.0 and modules (60+ pages) with a readable and correct description of the technology, what it is for and it's applications. It also includes an outline of how to create your own RSS 1.0 module and outlines how and why to reuse terms.
[I defer to others for how it address the non-RDF RSS flavours.]
The rest of the book contains an introduction to syndication, explanations of the server and client syndication aspects of RSS, publish and subscribe all with extensive examples and code.
Well done Ben - great work!
PS There are some minor typos, I'll let Ben know them for the Errata