I might be crazy, but I remember a supposed app a couple of years ago that used relative GPS so it could track your location even if you didn't get the best satellite coverage or there was nothing around you. You could plan a route based on landmarks in the environment around you instead of actual points of interest, so you could place a marker at the door of a building, for example. I think it was called breadcrumbs. I don't think it ever got released, but remember extensive documentation on it.
An app like this would be very useful to me now, as there is a building on my college campus that I need to locate quickly and accurately for a class change. Will blindSquare do this? I haven't taken the plunge yet and would invite suggestions.