Joakim Nygard has come up with a debug bar similar to ones found in other frameworks for the Zend Framework - the Scienta ZF debug bar.

The Scienta ZF Debug Bar is a plugin for the Zend Framework for PHP5. It provides useful debug information displayed in a small bar at the bottom of every page. Time spent, memory usage and number of database queries are presented at a glance. Additionally, included files, a listing of available view variables and the complete SQL command of all queries are shown in separate panels (shown configured with 2 database adapters):

You can check out an example setup here [png] and get the full installation instructions and latest downloads from the project's page.