On the NetTuts.com site there's a new tutorial showing you how to introduce the Memcached tool to your application - a quick and easy way to cache data and optimize performance.

Your latest PHP/MySQL website is finally online. And it's awesome. But it's not as fast as you want it to be, because of the many SQL queries running every time a page is generated. And above that, you have the feeling it will not scale well under heavy loads. And you are most likely right. In this tutorial, we will see how you can greatly improve your website's responsiveness [...] by implementing a cache layer between your code and your database. The good news is it is fairly easy, and can be done in a few minutes!

They help you get the memcached server installed (a one-liner in most linux distributions) and how to install the memcached extension using PECL. Code is included showing you how to connect to the server, store data into the cache based on a generated key and how to pull the same data back out.