I miss the shaderball only for one thing: Specular. Imho, a shaderball is very effective when it comes to define specular properties.
The render region is great, but I think that to tweak some "minor" effects (like specular and basic bump mapping) it becomes useless. The render regions is affected by what's in the scene, so even the slightest adjustment can take 5 minutes (or more) to update.
This is why I built a very simple rig. This is a nurbs sphere with a default phong shader. There are 3 infinites lights, whose intensities are controlled by a custom parameter set. Moving one slider affects intensity parameters for all lights.
Why 3 lights? Because 3 lights instead of one allow you to have a greater specular area on the surface.
So I putted the sphere and the lights under a model and exported it. Whenever I need to adjust a specular or define a bump I import this rig and apply the same shading model (phong, blinn, constant...) to the sphere as the real object. I hide everything expcept the import rig, so it's really fast!
Just my 2 cents
Bernard Lebel