This new tutorial from DevShed introduces something that could make a pretty profound impact on your application if used correctly - output buffering.

Output control (or output buffering) allows you to write and execute your scripts normally but send data to the web browser at selected times. The main benefit of this system is that you can call the header(), setcookie() and session_start() functions at any place in your scripts without having to worry about the "headers already sent" error message.

They start with the basics - the functions and what they do - then move on to an example, a login form, that uses the buffering to capture errors and html to be flushed and echoed at the end.