On the TutsPlus.com site they've continued their WordPress series showing you how to integrate class autoloading into your plugin development.

In this tutorial, we're going to take a break from writing code and look at what PHP namespaces and autoloaders are, how they work, and why they are beneficial. Then we'll prepare to wrap up this series by implementing them in code.

In the previous part of the series they built up the environment and some of the basic structure of the plugin (you'll need this to follow along with this new tutorial) and continue on, starting with the basics of namespacing and autoloading. They then move over and start applying this functionality to the plugin classes and what happens in the autoloader when they're referenced.