The basic thesis presented in the preface of Social Life of Information is this: you can tell that you've made a good tool, one that acknowledges and respects the social context of the user, if your users will fight to keep it in the face of competing technologies. Unfortunately, most tools don't endure or "fight back" in this way; instead, they "bite back," creating more problems than they solve. This kind of design is what the authors refer to as "tunnel design," where you focus exclusively on the information that you are presenting and ignore the deeper contextual information and values of users and the organizations of which they are part.
The authors, like Papanek thirty years before them, stress that it's important that everyone have an awareness of design, not just designers. Like Schumacher, they point out that we often overlook the infrastructure and social organizations that enable information. As long as it works well, this infrastructure is invisible, but recognizing and leveraging it is crucial to creating a good design that will "fight back."
Chapter 1 begins with some quotations, including this anonymous one that I don't agree with: "On an average weekday the New York Times contains more information than any contemporary of Shakespeare's would have acquired in a lifetime." (Perhaps it contains more worldly factoids than a contemporary of Shakespeare's may know, but I don't think it contains more information ...)
Despite the recent glut of information most who lament that we should return to "simpler times" when we weren't deluged with information wouldn't really want to do that - conveniences like phones, ATMs, electricity, and sanitation do make life much easier. (dag29580863 pointed out in the reading group meeting that it may be the rate of change of technologies rather than the technologies themselves that elicits anachronism.) This doesn't mean that these things can't be improved. Often, "improvements" consist of just adding more information (e.g. "how to use the help system"), or waiting until technologies that supply the information are bigger and faster, but both of these can and often do exacerbate the problem.
Organizations and other social structures - even things like paper (hence the predictions of paperless offices) - are seen by infoenthusiasts as impediments to information, rather than useful and important parts of our social lives. Information enthusiasts assume that the answers to all questions can be found digitally, online (e.g. Microsoft's "Where do you want to go today?"). Economists Downes and Mui said in the 1930's that organizations will only form and persist when they lower "transaction costs" of information, but despite the dramatic lowering of transaction costs recently, corporations are bigger than ever (and trans-national to boot) and distance universities have up to half a million students. (Maybe some of this is due to the scarcity of an ideas commons that Lawrence Lessig bemoans - present instantiations of intellectual property favor the large corporation with the extensive patent portfolio.)
Infoenthusiasts often think of people as just information processors that can potentially be replaced with computers, but in many cases people serve more functions than just information aggregation, filtering, and dissemination. Infoenthusiasts further claim that the digital age will naturally cause decentralization, but in reality centralization is easier than ever because messages can be sent across large distances so quickly and management structures don't have any reason to give up their power. People and social structures make information useful.