Rob Allen has posted a few notes about the Zend_Cache component of the Zend Framework to his blog today.
Recently I needed to speed up a legacy project that makes a lot of database calls to generate each page. After profiling, I discovered that 90% of the database calls returned data that rarely changed, so decided to cache these calls. One of the nice things about Zend_Framework is that its use-at-will philosophy means that you can use any given component with minimal dependencies on the rest of the framework code.
He shows how, using the Zend_Cache module (and friends Zend_Loader and Zend_Exception), he creates a caching class that can be called anywhere and is used to cache the results from the queries. His default lifetime is set to 7200 seconds - two hours - before the script needs to refresh the cache and get the latest updates.