Joseph Stalin is often credited with the aphorism that 'quantity has a quality all its own'. Presumably he was talking about tanks or steel at the time, but network effects are similar, as is coverage. My 2010 prediction is that we will see this effect in the photo services (probably Google's first). As more photographs are made public and more metadata about the pictures is available, these services have the possibility of doing very interesting things with the data. In 2007 Microsoft demonstrated what they could do with Flickr photographs of Notre Dame in Photosynth, automatically making a montage of the overlapping photos that you can view from any perspective.
I'd say that we are rapidly approaching the point where much of the earth has been photographed in detail. As more of the photographs are made public and tagged with position metadata automatically applied by cameras with GPS receivers, it will become ever easier to patch them together into a seamless (or at least well-seamed) view of the world. More than that, it should be possible to start to recognize the relative age of the photographs so that you can move back through time to see historical views, use the people tags that Picasa encourages you to add to photos to identify even more people, and do many more things by processing the metadata and images.
As I sit here contemplating buying a Nexus One phone from Google I can't say I'm enthusiastic about entrusting my whole life to one company, but I expect they are trying to do this sort of thing right now.
In libraries we are seeing similar effects as more of our materials are digitized. One of my long term predictions has always been that everything in libraries would eventually be digitized, although I had no idea that a company like Google would be doing so much of it. Digitization will probably really take off when it can be done without opening bound volumes at all, by doing high resolution CT-scans and parsing them into pages.
The graphic is from the current (January 2009) VIAF record for Joseph Stalin. We are linking together 13 different authority files that have an entry for him, plus finding a link into Wikipedia. This level of coverage (we have VIAF records representing nearly 10 million people from 20 different authority files) has implications on the sort of matching and services that can be done on names. Probably not as showy as stitching the world in photographs together, but important nonetheless.
Those of you who follow Stu Weibel's blog may remember this post. I claim that the first time I heard the phrase about quantity and quality was from Stu, not the other way around.