I didn't mean to buy this book but I'm so glad that I did. Although I've made use of XMPP as yet-another-IM-service I'd never bothered to look 'under the hood'. Put simply, this well written book (packed with pertinent examples) has opened my eyes to the potential of XMPP as a platform for application development.
Each chapter builds upon and is a logical progression from previous chapters and material is simply explained and illustrated with appropriate examples of XML and Python. I especially like the choice of Python since it looks like pseudo-code and is thus friendly to developers who use other languages. Another plus is how the authors promote the XMPP development mindset rather than just explain how stuff works. For example, don't change core behaviour, keep complexity at the server, re-use existing protocols and so on.
My only (very minor) gripe is wishing that the example application introduced in the final chapter was longer and bigger in scope so that more stuff could be demonstrated with a practical example. Mind you, I suppose that's just me saying I'd have liked yet more of the same.