Gergely Hodicska has posted about some hacking he's down with the Zend_Acl package in the Zend Framework to make support for custom roles and resources.
I found that the base Zend_Acl package has some limitation/problem if you want to use it in a bigger real life project. Zend_Acl supports only logical roles, resources so I decided to extend it to allow using custom roles and resources which can represent existing entities (for example users/groups and topics in a database)
He talks some about the package and its current functionality, including the limitations he ran up against. He came up with a structure for what he wanted (seen here) and set out to extend the class, making an interface and implementing it with his own loading method.
His source code can be downloaded here.