The ratio who have not heard of Jehovah's Witnesses is FAR higher than 50%. I have lived and traveled extensively in the 3rd world, I met very few people outside of major cities who had ever heard of Jehovah's Witnesses. I met NO ONE in Papua New Guinea who had ever heard of them. Same goes for Afghanistan, Iraq, and Pakistan. My brother also travels extensively in the 3rd world. He says the same thing.
As for America goes, anytime I mention Jehovah's Witnesses to people they either act like I just said "Assyrians", in that yes they have heard the term but have no idea what the people might be like, or they say "Oh the cult".
I'm not a Christain, but it seems to me that if the door to door preaching work was a "God directed" work as the WTBTS claims then all those billions of hours spent in the door to door work might at least result in people being educated as to what the Good News that they are supposedly preaching actually is.