Monkeyboi, you can select object who cast shadows ! With the 'Tracaeble option of the material
In fact, I wrote this in the case you want to use that feature to add dirt because you're not suppose to add this effect to all objects.
Of course, we can always modify the 'ambient' intensity of a material to change the power of the dirt, but it will change the intensity of the lightning for this object and this is not what we want to do.
No, exactly, and that was my point. It would fit better in the Render Buttons because it is a rendering feature just like 'Shadows' is. Ofcourse it was even more flexible when it was a light becase you could have several AO passes and you could control the energy factor etc, but it surely doesn't make sence in the World buttons.