In a new post to his blog Nick Belhomme takes a look at namespaces in PHP 5.3 - what they are and how to use them (complete with code snippets of a small sample project).
With PHP5.3.3 recently released I really feel it is time that php developers are taking namespaces seriously. If you don't I guarantee you will be out of a job within five years. Namespaces are a fundamental part of the future of PHP.
He also makes his sample project available for download so you can follow along a bit better. He shows how to create a namespace, how to use them in both simple and more complex examples.