For me, it is THE differentiating feature that keeps me using Google maps, rather than a competing service. I take an annual 7 day motorcycle trip though the southwest US, and street view allows me to see a road from ground level which is far more useful that satellite view to determine the road contours, and whether it would be a nice ride. Admittedly, in all the places I ride, street view hasn't been updated since 2008, so its no longer useful to identify business, but its still quite useful.