Ken Guest has posted about a whitepaper that he was involved in editing - the PHP for Enterprise/Business Whitepaper:

As far as I know this is the first full English language translation and update of the work done by the Association Francaise des Utilisateurs de PHP (French PHP Users Group). Also there is a lot of new content in the Whitepaper that with regards to how PHP is now utilised in Enterprise. Figures have been updated and techniques available in later versions of PHP have been referenced.

He mentions some of the challenges in the translation and thanks a few others for the effort and contributions they made to the project. The whitepaper (pdf) looks at several key topics of PHP in the Enterprise including: suggestions for architecture, integration issues, concurrent use with other languages and how PHP fits into the web application ecosystem.