On PHPBuilder.com today there's a new tutorial from Jason Gilmore about using the SPL with different data types to more effectively work with them more effectively.

One great way to incorporate more OOP into your applications is through the Standard PHP Library (SPL), a powerful yet largely unknown extension made part of the official PHP language with the PHP 5.0 release. [...] In this tutorial I'll introduce you to several of my favorite SPL iterators, providing you with the basis from which you can continue your own exploration. Following several examples, I'll conclude with a brief introduction to other key SPL features.

He looks at how to use the ArrayIterator, DirectoryIterator, SimpleXMLIterator and mentions some of the other handlers for things like advanced data structures, exceptions and more file handling.

In a new post Havard Eide looks at the creation of a Countable interface that can be used in any application:

Today I will look at the Countable interface, it has a single function that needs to be implemented: count(), by implementing this you can ensure that there is a count() function ready to use on any given class that implements it. The Countable interface is used in other places in the SPL as well: the ArrayIterator and ArrayObject classes implements this interface ( and SqliteResult if present ).

In his code examples he shows simple methods for returning the count() of a property, but notes that the real power of it comes in the ability to manipulate the number returned from the call based on other parameters (or filtering).