If you just can't get enough information on the Zend Framework and are looking for a good overview of where it's come from and where it's going, you should check out the latest issue of php|architect magazine with the cover article from Mike Naberezny.
From his blog:
In the article, I begin by introducing Zend's motivations for creating a framework and how it relates to their PHP Collaboration Project. More information on these topics can be found on the Zend Framework website. I then dive into a tutorial where I take a business scenario and show how the components included in the Zend Framework can be put to work.
The article demonstrates a workflow where invoice data is retrieved from a web service, an invoice in PDF format is then built from that data, and finally the resultant file is emailed to a customer. The components Zend_XmlRpc_Client, Zend_Pdf, Zend_Mail, and Zend_Search_Lucene are explored along the way.
You can purchase both a print and electronic (PDF) copy directly from the php|architect site - no need to subscribe and a single issue only costs $3.50 USD.