From WebReference.com this morning, they have the next posting from the PHP Anthology book - <a hrefhttp://www.webreference.com/programming/phpanth3/">Volume 2: Applications. Chapter 5: Caching

In the good old days, back when building Websites was as easy as knocking up a few HTML pages, the delivery of a Web page to a browser was a simple matter of having the Web server fetch a file. A site's visitors would see its small, text-only pages almost immediately, unless they were using particularly slow modems. Once the page was downloaded, the browser would cache it somewhere [...] the advent of dynamic Web pages spoiled the party, effectively "breaking" this model.

Of course, since dynamic pages are constantly changing, the author definitely benefits from reloading the page each time it's requested. He gives several methods and ideas to help keep your viewers from caching important pages, template caching, and "chunked buffering".