Leonid Mamchenkov has posted a "quick and easy introduction" to PHPMD, the "PHP mess detector" tool. PHPMD automatically scans your code looking for potential issues including "suboptimal code, overcomplicated expressions and unused parameters, methods, properties".
PHP Mess Detector is yet another one of those tools that help to keep the code base manageable and clean. Here is how you can jump right in. It’s super easy. It only takes 6 steps.
He gives an example of it in use on a CakePHP plugin showing the process to install, execute and view the report it provides. He looks in detail at one of the issues it found, an unused local variable, and how he fixed the issue and pushed the result back to the main repository. He finishes up with some suggestions about ways to run the tool, integrating it into your automated workflow and using it on other Open Source projects to find "low hanging" issues to fix and contribute back.