Before I voice my opinion, a disclaimer: I have met Cal personally; in fact I'm having diner with him next Monday, I'm writing a book for php|architect, and my company is a Zend partner. I could not be any more biased. If you still trust my judgement (and I will try to remain objective), read on.
Ivo mentions the important things - like how fun the book is to read (a book about a framework, who knew?) and what sort of things it covers. Components of the framework are mentioned but so are things like caching, layouts and web services. I'd give away the ending but that wouldn't be any fun so go check out his unbiased opinion of hos the book turned out.