By Mark Ward
BBC News Online technology correspondent
The net is being used to summon up spontaneous crowds that are being put to artistic, charitable and social ends.
The power of the crowd is starting to be tapped
The craze began in New York in June.
Many of the city's net literati were invited by e-mail to take part in an art event that called itself the Mob Project.
The e-mail asked people to synchronise their watches and wait at 7pm in one of four of Manhattan's bars.
Once there, co-organisers of the mob handed out instructions of where the full mob should meet.
The first mob, which involved 100 people, convened in the ninth floor rug department of Macy's department store and gathered round one particular carpet.
Any member of the mob approached by a sales clerk was told to say they all lived together in a warehouse on the outskirts of New York and wanted a love rug to play on.
The second mob, of 250 people, took place on 2 July and initially gathered in Grand Central Station.
However, the huge police presence persuaded the mob organisers to move it to the mezzanine of the Grand Hyatt hotel next door.
This time no rugs were involved.
Instead at 7:12 the 250 mobsters broke into spontaneous, thunderous applause for 15 seconds. Then, its job done, the mob dispersed.
"It's just about doing something fun," said David Danzig, a New York blogger and vice-president of Charge.com, who took part in the Grand Hyatt mob.
Some artists have put mobs to their own ends
"I get the impression that it's a performance art piece," he said "but I think that more than that it is just supposed to be silly in the way that performance art is supposed to be."
The next New York mob is planned for this week.
The spontaneous gatherings have been given various names such as "smart mobs" and "flash crowds". The latter term derives from a 1973 science-fiction short story by Larry Niven.
In the story teleportation was common and a "flash crowd" described the sensation seeking mob that suddenly teleported in to places where crashes or other disasters had taken place.
Meeting of minds
Conjuring up a mob is catching on.
Now there are mobs planned for San Francisco, Minneapolis, Texas, London and Dutchess County in upstate New York, all organised by different people.
"We don't know if this is a full-fledged movement or just some geeks having fun," wrote the Dutchess Mob organisers in an e-mail to News Online.
"Ask us again in a year and we'll probably have a better answer on that aspect of this phenomenon," they wrote.
The Dutchess organisers want to use the spontaneous mob as a way of reflecting the continual surveillance of people on the street and online.
Rob Zazueta, who is organising the San Francisco mob via the Flock Smart website, sees the potential for these spontaneous crowds to have an effect beyond the merely aesthetic.
He envisions a mob being organised to go along to a charity drive and drop off food, clothes, toys or whatever else is being collected en masse.
But, he says, the main reason for mobs getting together is purely social.
Supporters of US politician Howard Dean co-ordinate via the web
He said a lot of people now spend a lot of their lives behind computer screens talking to and exchanging messages with people, often close friends, who they never see in person.
"This is a way of evolving that computer social interaction back to reality," he said.
The idea of using the net to co-ordinate groups of people is not new.
Many political protesters use e-mail, or phone text messaging to co-ordinate demonstrations and outflank the police or just to keep a campaign rolling.
Potential US Democratic presidential candidate Howard Dean is using the Meetup.com website to organise support.
Such spontaneous gatherings have precedents in the actions of 60s counter cultural groups such as the Merry Pranksters.
This time the technology makes it much easier to contact the community and get it moving. It could mark the start of the largely unseen net population realising the latent power of its millions of members.