So rough gold would be completely black? I don't know, roughness doesn't change anything about the reflectivity of the material, just the "blurriness" of the reflection. So on metals or at grazing angles you'll lose an incredible amount of lighting if you simply turn it off for rough materials. If anything I'd approximate rough reflection using an approximation via a diffuse term.
No need for that. Even though every material reflects light, there's no need to waste computation time calculating reflections for rough materials because the reflection won't be noticeable.
Oh, my bad. I thought he was talking about the specular power used in the BRDF.
Its common to store a glossiness value in the range [0,1] in textures and then convert it to specular power using a function like this:
float specPower = pow(2.0f, 13*glossiness);
Ambient occlusion is low-quality shadowing information. Use it on anything non-directional, where you don't have better visibility information. So don't apply it to reflections or any point / spot / directional lights. Just to irradiance or other kinds of ambient terms, like diffuse sky illumination. Basically every source of light which comes from more than just a single direction (this includes area lights) could be multiplied with ambient occlusion. The more it spans the hemisphere over the surface, the more it's suited for ambient occlusion. Environment maps might span the whole hemisphere over the surface, but when used for reflections, only a single direction is used, so you shouldn't apply ambient occlusion to it. If the environment map is used for diffuse image based lighting, samples over the whole hemisphere are used and thus ambient occlusion should be applied. For rough reflections you might want to blend in ambient occlusion to some degree though.
So would it be correct to multiply this by the ambient occlusion ?
I'm not quite sure which shadows you're talking about. But basically you are "tracing" a reflection ray and the environment map helps you find the intersection. So there's no need for any kind of shadow map.
And how about shadows ? Do I multiply or add them to the environment map color ? Or not at all ?
Either it's actually too strong or the reflection is not rough enough. Hard to tell without seeing the result.
But even with a fresnel reflectance color of 0.028f (for skin) I'm seeing reflections even when not at glancing angle on the skin. Do you think the color of the env map is too bright ?