In a new post on Chris Renner's blog, Chris discusses his experiences in implementing Zend_Registry as a stand-alone module in his appliciations.

Zend_Registry is a very lightweight module (one file), that is actually an extension to the native ArrayObject PHP5 class. Any variable, object, or scalar you load into Zend_Registry instantly becomes available globally throughout your script. Let me prevent confusion by saying there is no persistence across page loads--this is just for within each request--but the upside is any scope issues are swept away in a very elegant manner. Hint: Combine Zend_Registry with Zend_Cache to achieve persistence.

He goes on to describe extending Zend_Registry in order to directly access elements or properties of arrays and objects stored in the registry using static methods.