On PHPMaster.com today there's a new tutorial posted that wants to guide you through the world of aspect-oriented programming with a CodeIgniter application as a base.

Have you ever heard of Aspect Oriented Programming (AOP) before? It’s a widely used concept in developing enterprise level systems, although it hasn’t seen much use in PHP. I’m going to use this article as an opportunity to introduce PHP developers to AOP. This tutorial will be delivered to you as a 3-part series. In this part I’ll explain the concepts of AOP. In part 2 I’ll show you the practical uses of AOP and creating a AOP rules structure. Finally, I’ll show you how to integrate AOP functionality using CodeIgniter in part 3.

Since this is just part one, they mainly focus on some of the key points of AOP like aspects, advice, jointpoint and pointcuts. For each, there's brief descriptions for the types and, for some, code samples showing the idea in action.