The Developer Drive site has a new post with a few beginner suggestions about how to do some error reporting in your applications:

As much as programmers attempt to anticipate every possible action or combination of actions that a user can take when encountering a web application, no one can foresee them all. When the user takes an unanticipated course of action and "breaks" the application, the software needs to catch them before they fall.

They show you a few methods for handling the errors that might come up including the die function, exception handling, triggering errors and just outputting errors via an "echo" or "print" (or something similar).