Did you know that Zend Server not only has it's own PHP accelerator built in (like APC). But that it also has similar functionality allowing for caching of data in shared memory? Shahar Evron, Project Manager of Zend Server, has written a white paper describing just how exactly to use this to good effect.
Caching is one of the simplest ways to increase the speed of your application and Zend Server makes it simple with its included Optimizer+, Zend Page Cache and Data Cache API tools. For more information, you can download the whitepaper here [pdf].