30% all around in a sedan...
daytime: its like a shade, you can see what is going on inside the car still. not the greatest for daytime mostly when its hot and sun is in your face. but then, its better than nothing. pick you nose, ppl will laugh
night: 30% is perfect for night imo. its not wankster dark, but dark enough to the point where you can barely know whose inside. pick your nose, ppl will laugh but wont know who it is.
and i agree w/ going same percent all around. it looks off when ppl do real dark in rear and light up front (like me

)