Another thing I've been thinking about is how to make a webCMS that is a mix of CMS managed static content and dynamic content. Say, you know the information on a page is pretty stable, so you want to burn it to the file system instead of making database calls each time, a la Bricolage. Are caching systems like the Zend Engine the best of both worlds?

Interesting Related: Zend.com on using PHP for user readible URLs.