As a first step towards more physically plausible materials, I've added new energy conservation mode that automatically dims diffuse color as reflection is increased. It should be faster, simpler, more realistic, and is consistent with what mental ray and vray does.
Because it changes the way materials render, it is disabled by default so existing scenes do not break. Any newly created materials have this mode however enabled. It is a simple checkbox in advanced material tab, so you can switch it any time.