On PHPBuilder.com there's a new article on OOP in PHP applications, specifically some of the things that PHP5 has to offer you if you're not using it to its fullest potential.

I'll introduce you to three of PHP's advanced object-oriented features which seem to not have garnered the attention they deserve. The topics discussed here should be useful whether you're a relative newcomer to object-oriented development and are looking to expand your knowledge, or have a background using languages such as Java or C# and are trying to learn more about what PHP has to offer.

These three things he introduces are Reflection (PHP's API for introspection of code), the SPL (Standard PHP Library) set of objects and tools and a more recent addition - late static binding.