Near Near Future has an interesting post about thinking carpets. A self-organising network integrated into the floor registers and deals with a variety of sensory input. Different distributed sensors could do things as diverse as coordinate climate control, spot fires, direct people to emergency exits and the emergency services to disabled casualties.
However, what the post doesn't talk about is what would happen if these sensors weren't just passive, but interactive. If you embed a Bluetooth chipset into them then you immediately get into the realms of ubiquitous computing and augmented reality.
Combine the data from a ubiquitous sensor network with your own GPS fix, access to interesting location dependant and environmental data, and you have a powerful tool. Integrate this into a collaborative agent architecture linked together via Bluetooth, where the agent running on your mobile phone or wearable computer can talk to other nearby agents which could belong to passers by and you have more than a powerful tool, you have a paradigm shift in the way we look at the world.
We move through a sea of data, but until recently most of it was opaque, stuck in proprietary formats, hidden, or simply unavilable to the user. However with the arrival of peer-to-peer systems, and short range wireless networks, we are moving rapidly towards ubiquitous computing whether you like the idea or not. Personally, despite the possible privacy concerns, I think it's a good thing. Perhaps if everyone has ubiquitous access to all the data then the question of "Quis custodiet ipsos custodes?" becomes irrelevant. Of course the trick is to try and ensure that you have access to all the data...