Yes it can be done with shaders--to a degree. You still couldnt put two lights above a plane side by side and have it work. Imagine a shiny plane with two lights above it side by side. Lets say that you dont want specular highlights from the light on the left, you just want it for some more light. Reducing the specularity in the shader for the plane will not remove the specular highlight from the left light, it will only increase or decrease both equally. So now you will have two hotspots on your shiny plane. I have found this to be a nice feature in Lightwave, especially when doing outdoor scenes, say with a logo floating above an ocean. The distant light wasnt lighting the logo enough, but the ocean would look great. If I add another light it also affects the specularity of the ocean. Selective lighting can solve that too, but a switch that specifies if a light affects specularity, diffuse or both would be nice. Also, I have run into scenes where all I wanted was a bit more specularity--but not brighter specularity that already existed. With a switch I can throw another light in there, not worry about the diffuse getting too bright and place that light where I want to get another highlight. Again, it can be worked around, especially now that Carrara does have selective lighting options. But IMHO it is much easier and quicker to have a switch for the light dialog.