As Ed Finkler points out there's a new article posted (written by him) on the C7Y site (from php|architect) talking about his Inspekt library - an introduction to the filtering library showing how to help make your applications safer.

Inspekt is a library for PHP4 and PHP5 that aims to make safe input handing easier, and unsafe actions more difficult. Inspekt establishes a new development approach by wrapping input within "cage" objects, and requiring the developer to use validation and filtering methods to test and manipulate the input data. This article provides a brief introduction to Inspekt and its capabilities.

The article covers all of the basics - what the library can do for you, how it integrates into your application and how it helps to protect you from potential problems with the data in your superglobals ($_GET, $_POST, $_REQUEST, etc).