If you develop web apps, I encourage you to check out The Twelve-Factor App. This is an excellent resource for anyone building and deploying software-as-a-service. PHP has great support for many of the twelve-factors. I want to take a look at specifically how each factor may be applied to a PHP application.

Some of the points the Twelve-Factor App makes aren't entirely relevant to PHP (like "Backing Services") but Bradley gets into details on others, providing technology that can be used to fill the need.