Most of the big Web 2.0 websites rely on memcached (pronounced "Memcache-Dee") to scale, even the ones not using Rails. In this screencast you'll learn how easy it is to use memcached in your Rails application, and how to do low level query caching for websites where you have highly customized layout...

If there's no way to cache the entire content of a page, then odds are you can probably cache smaller pieces of it. This is where fragment caching comes in, allowing you to cache common parts of a webpage which are resource intensive and may be used accross mulitple pages.