On the ITNewb.com site there's a recent tutorial posted covering the use of JSON in PHP applications - on both the creating and parsing sides.

So you've heard the fanfare over JSON, but still haven't had the opportunity to dive into using it. Well, as a matter of fact, you may have been using JSON all along and not known it. Compounded by the fact that since PHP 5.2 there is native support for JSON, learning how to send data between your client and your server just got a whole lot easier.

He starts off with a look at what JSON is and some examples of the syntax. For his examples he uses the Twitter API's JSON output format to get tweets from a user's timeline. The json_encode and json_decode functions are used on the PHP side to handle the "heavy lifting".