Please make 'Shading Groups' the thing you assign to objects. Currently you assign materials to object, which are displayed a shaders, for example a lambert or a phong. In order to assign a new material, you have to do it through the shader. When in fact, the shading group (and all its inputs) is what gets assigned. This is very confusing.
In addition I would recommend getting rid of the 'shading group' name and replace it with 'material' like in Softimage.
