From an article at
Science News: "People making travel plans may unwittingly heed a strange rule of thumb - southern routes rule. In a new experiment, volunteers chose paths that dipped south over routes of the same distance that arched northward, perhaps because northern routes intuitively seem uphill and thus more difficult, researchers suggest."
In other words, most people intuitively think that north == up. Zoro is vindicated!!! Okay, not really. His sense of direction still sucks. But everyone else's sucks a bit more! I bet Nami would have aced the experiment though.
Isn't it sad that when I read the article the first thing I thought of was One Piece?