@Flubba, does this allow me to have folders inside my include directory? flat include directories give me nightmares. as the whole objects directory should be in the inc directory.
Oh yes, absolutely. So for example, we use a single layer of subfolders, generally:
require_once('library/string.class.php')
You need to be careful with relying on the include path too much in really high traffic sites, because php has to hunt through the current directory and then all the directories on the include path in order to see if your file is there and this can slow things up if you're getting hammered.
So for example if you're doing MVC, you'd put the path to your application directoy in the include path and then specify refer to things in the form
'model/user.class'
'controllers/front.php'
or whatever.
But generally speaking, it just lets you work with really short paths in your PHP that will work from anywhere and it's a lot easier to read than all that realpath document root malarkey.
The benefit of those script-based alternatives others have suggested is they work anywhere, even on shared boxes; setting the include path requires a little more thought and effort but as I mentioned lets you start using __autoload which just the coolest.