There are multiple forms of depth perception. There is stereoscopic depth percetption, which is what y'all are talking about, and is the most "innate," if you will, form of depth perception. However, there are others (which we process subconciously) such as knowing which object is in front of another and realizing the one in front is closer, leading lines (e.g. things growing smaller in the distance), speed (when moving or for moving object only, of course), relative size combined with our knowledge of the size of most things, plus several more. So, I guess some people might not have these other forms of depth perception function as well (since they're more of an aid of sorts), but for the most part you should be able to get by with one eye just fine. Really it's only an issue within about arm's reach, because as things grow closer to your face, the disparity of the image between your two eyes grows and gives us the ability to know how close something is up close. At a greater distance, though, focal lengths are longer and the image disparity is much smaller, meaning for (most) driving, you use the main form of depth perception less than some others.
