(Please see update at bottom.) I am grateful to Michael Ham, of the Later On site, for a tip about an amazing photographic site that makes one consequence of technology far more vivid to me than it had been before. If you haven't yet seen it, please follow along.
The technology in question starts with "gigapixel" photography. Gigapixel photos are giant panoramas that themselves consist of hundreds of component mega-pixel digital shots. This means that you can begin with, say, a distant view of London or Seville or San Francisco -- and then keep zooming in until you are looking at individual buildings, cars, street signs, people. It's the effect we've come to take for granted with Google Earth, but with much greater close-in photographic clarity.
When you combine that with better and better automated systems of matching faces to real identities, plus human-run social-network tagging systems, what do you have? The result is something familiar in dystopian sci-fi novels from 1984 onward but until now not part of real life: the impending extinction of the "faceless crowd" and removal of any mask of anonymity as we go about our daily affairs.
If you go to this site, you'll see what I mean. It starts with a big crowd scene in Vancouver, soon before the Stanley Cup riots, which were at this site and presumably involved some of these people. If you start zooming in on the photo, you can get close enough to almost any of the tens of thousands of faces to see who it is.