The PHP::Impact blog has a quick performance tip posted today for all of the Zend Framework-ers out there that are seeing some poor performance with their Zend_Controllers.
Zend_Controller_Front gets an instance of Zend_Controller_Router_Rewrite, routes the request, iterates through all the provided routes and matches its definitions to the current request URI. The problem with this is that the more routes you add, the more time the router will take to find a positive match.
Federico includes a few benchmarking stats to back this up ranging from four routes up to forty. His solution is to place the routes in different files and set the location with a Zend_Config_Ini object. This makes the controller only load the ones that are needed instead of pulling all forty into memory to have to parse through.