In today's tutorial, we're going to mix a handful of technologies. First, we'll review how to implement a simple form of text file caching with PHP. To illustrate this technique, we'll use the wonderful YQL to query Twitter's search API for a list of tweets which contain the string, "nettuts." Finally, we'll experiment with PHP's regular expression capabilities, and will turn all Twitter usernames and urls into clickable links.

They show you (with the help of a few screenshots) how to get the YQL system to work with your PHP scripts and how you can fun a simple query against it. They use a simple file-based caching technique and a regular expression (not the simplest thing, mind you) to extract usernames and links from the results.