I think it would be a good idea to have an option linked to the Layer properties which says any input is directed at that layer.
In other words if you want to click an object the click only applies to the selected layer. Also if the layer is marked as hidden then the objects on that layer cant be selected.
I know you can do this by checking whether the layer is visible etc but it would just save time. <img src="smileys/smiley1.gif" border="0" align="middle" />