There are criticisms that require_once/include_once are slow. To speed up them, I find this solution from http://www.php.net/require_once
antoine dot pouch at mcgill dot ca
require_once (and include_once for that matters) is slow.
Furthermore, if you plan on using unit tests and mock objects (i.e. including mock classes before the real ones are included in the class you want to test), it will not work as require() loads a file and not a class.
To bypass that, and gain speed, I use :
class_exists(‘myClass’) || require(‘path/to/myClass.class.php’);
I tried to time 100 require_once on the same file and it took the script 0.0026 seconds to run, whereas with my method it took only 0.00054 seconds. 4 times faster ! OK, my method of testing is quite empirical and YMMV but the bonus is the ability to use mock objects in your unit tests.