Nicholas Carr's fourfold typology of Crowds :
Social production crowd
consists of a large group of individuals who lend their distinct talents to the creation of some product like Wikipedia or Linux.
acts essentially as a survey group, providing an average judgment about some complex matter that, in some cases, is more accurate than the judgment of any one individual (the crowd behind prediction markets like the Iowa Electronic Markets, not to mention the stock market and other financial exchanges).
Data mine crowd
a large group that, through its actions but usually without the explicit knowledge of its members, produces a set of behavioral data that can be collected and analyzed in order to gain insight into behavioral or market patterns (the crowd that, for instance, feeds Google's search algorithm and Amazon's recommendation system).
a group that trades information through a shared communication system such as the phone network or Facebook or Twitter.
Clay Shirky, who is also participating in the discussion, suggested a fifth crowd type for this list:
"Transactional crowd": a group used to instigate and coordinate what are mainly or solely point-to-point transactions, such as the type of crowd gathered by Match.com, eBay, Innocentive, LinkedIn and similar services. (I would think that contests like the Netflix Prize also fall into this category.)"
A group organized through online communication for a particular event, which can take place either online or in the real world and may have a political, social, aesthetic, or other purpose." (http://www.roughtype.com/archives/2010/03/a_typology_of_c.php)
Analyzing the negative aspects of political crowds
"n trying to understand how and why crowds go wrong, you can have no better guide than Clifford Stott, senior lecturer in social psychology at the University of Liverpool. Stott has risked his life researching his subject. Specifically, he has spent most of his career—more than 20 years so far—conducting a firsthand study of violence among soccer fans. On one particularly dicey trip to Marseilles in 1998, Stott and a small crowd of Englishmen ran away from a cloud of tear gas only to find themselves facing a gang of 50 French toughs, some of them wielding bottles and driftwood. “If you are on your own,” a philosophical fellow Brit remarked to Stott at that moment, “you’re going to get fucked.” This, in a sense, is the fundamental wisdom at the heart of Stott’s work—though he does couch it in somewhat more respectable language.
To Stott, members of a crowd are never really “on their own.” Based on a set of ideas that he and other social psychologists call ESIM (Elaborated Social Identity Model), Stott believes crowds form what are essentially shared identities, which evolve as the situation changes. We might see a crowd doing something that appears to us to be just mindless violence, but to those in the throng, the actions make perfect sense. With this notion, Stott and his colleagues are trying to rebut an influential line of thinking on crowd violence that stretches from Gustave Le Bon, whose 1895 treatise, The Crowd, launched the field of crowd psychology, up to Philip Zimbardo, the psychologist behind the infamous Stanford Prison Experiment of 1971. To explain group disorder, Zimbardo and other mid-20th-century psychologists blamed a process they called deindividuation, by which a crowd frees its members to carry out their baser impulses. Through anonymity, in Zimbardo’s view, the strictures of society were lifted from crowds, pushing them toward a state of anarchy and thereby toward senseless violence.
By contrast, Stott sees crowds as the opposite of ruleless, and crowd violence as the opposite of senseless: What seems like anarchic behavior is in fact governed by a shared self-conception and thus a shared set of grievances. Stott’s response to the riots has been unpopular with many of his countrymen. Unlike Zimbardo, who would respond—and indeed has responded over the years—to incidents of group misbehavior by speaking darkly of moral breakdown, Stott brings the focus back to the long history of societal slights, usually by police, that primed so many young people to riot in the first place.
Meeting Stott in person, one can see how he’s been able to blend in with soccer fans over the years. He’s a stocky guy, with a likably craggy face and a nose that looks suspiciously like it’s been broken a few times. When asked why the recent riots happened, his answers always come back to poor policing—particularly in Tottenham, where questions over the death of a young man went unaddressed by police for days and where the subsequent protest was met with arbitrary violence. Stott singles out one moment when police seemed to handle a young woman roughly and an image of that mistreatment was tweeted (and BBMed) throughout London’s black community and beyond. It was around then that the identity of the crowd shifted, decisively, to outright combat against the police.
Stott boils down the violent potential of a crowd to two basic factors. The first is what he and other social psychologists call legitimacy—the extent to which the crowd feels that the police and the whole social order still deserve to be obeyed. In combustible situations, the shared identity of a crowd is really about legitimacy, since individuals usually start out with different attitudes toward the police but then are steered toward greater unanimity by what they see and hear. Paul Torrens, a University of Maryland professor who builds 3-D computer models of riots and other crowd events, imbues each agent in his simulations with an initial Legitimacy score on a scale from 0 (total disrespect for police authority) to 1 (absolute deference). Then he allows the agents to influence one another. It’s a crude model, but it’s useful in seeing the importance of a crowd’s initial perception of legitimacy. A crowd where every member has a low L will be predisposed to rebel from the outset; a more varied crowd, by contrast, will take significantly longer to turn ugly, if it ever does.
It’s easy to see how technology can significantly change this starting position. When that tweet or text or BBM blast goes out declaring, as the Enfield message did, that “police can’t stop it,” the eventual crowd will be preselected for a very low L indeed. As Stott puts it, flash-mob-style gatherings are special because they “create the identity of a crowd prior to the event itself,” thereby front-loading what he calls the “complex process of norm construction,” which usually takes a substantial amount of time. He hastens to add that crowd identity can be pre-formed through other means, too, and that such gatherings also have to draw from a huge group of willing (and determined) participants. But the technology allows a group of like-minded people to gather with unprecedented speed and scale. “You’ve only got to write one message,” Stott says, “and it can reach 50, or 500, or even 5,000 people with the touch of a button.” If only a tiny fraction of this quickly multiplying audience gets the message and already has prepared itself for disorder, then disorder is what they are likely to create." (http://www.wired.com/magazine/2011/12/ff_riots/all/1?)