Fabien Potencier has written up a new post about two features of PHP he thinks are underused and very powerful - iterators and streams.
PHP also have a lot of awesome features; at least two of them are in my opinion largely underused: Iterators and Streams. You won't learn how to use them in this post, but with a simple example, I hope you will want to learn more about them.
He gives an example of a recent update he made to the sfFinder class for Symfony to use iterators instead of the current implementation. With the help of streams, making it translate its searching skills from the local machine out to an Amazon S3 instance was a relatively simple change to the stream's location.