Josh Adell has a new post today looking at the "powerful combination" of using traits and interfaces in PHP applications. He shows how, despite traits not implementing the interface directly, they can be used to make other classes adhere to them simply by "using" them.
If you're not using interfaces in PHP, you are missing out on a powerful object-oriented programming feature. An interface defines how to interact with a class. By defining an interface and then implementing it, you can guarantee a "contract" for consumers of a class. Interfaces can be used across unrelated classes. And they become even more useful when combined with the new traits feature in PHP 5.4.
He illustrates with a package shipping example and uses an "Addressable" Interface to define the structure for both a Company and Users class. He includes code showing how to implement it in a more traditional "implements" way in a class, but also shows an interesting way to achieve the same thing with traits. Having a trait that follows the interface makes it easy to have a class adhere to the interface just by including the trait (or "using" it).