The skyline barrier tool uses a light source with parallel light (sun). However for many applications only a point-shaped light source would work. An example would be calculating the effect of 3D Models (barriers) for radar surveillance or the effect of street lights in a city model. A simple parallel/point light source switch buttton would help :-).
Additionally it would help quite much if we could use 3D models in the viewshed analysis tool as well (GlobalMapper can do this...)