The impacts of smart mob technology already appear to be both beneficial and destructive, used by some of its earliest adopters to support democracy and by others to coordinate terrorist attacks.
From the Sacramento Bee:
Two months after the Westfield Galleria in Roseville closed from a devastating fire, shoppers were again forced to evacuate Monday. This time, choral singers are to blame.
The Sacramento Choral Society and Orchestra and several area congregations had prearranged a "flash mob" singing of the "Hallelujah Chorus" in the mall's food court.
But with thousands of people crowding the second-floor food court, the "random act of musical kindness" never got off the ground.
"It was so jammed with people that you could not even move," said Connie Santos, who hoped to enjoy the music, then shop...
Somebody reported hearing two pops that sounded like the floor was giving way and another said the floor was shifting," said Tom Dodaro, a Roseville Fire Department spokesman. Read full article
Choral flash mobs are now a common occurrence, as this group of videos will attest to, but none have been so earth-shaking thus far.
The Sacramento Bee has posted a video of the incident, embedded here, in which you can hear a police officer directing people to clear out, saying "We have a serious safety issue right now...Please move back. You can keep singing, but please move off."
Later, someone from the Sacramento Choral Society says, "I think that people were happy to have the chance to sing the Hallelujah Chorus...We did it outside. It was a glorious experience. We must disperse this crowd now. This is really quite out of control."
On the Sacramento Bee site, there's quite a lively debate going on as to the wisdom of organizing the event (not to mention side arguments about separation of church and state).
One of the more interesting articles I've read about flash mobs was this one, from Harper's in 2006, written by someone who claims to have invented the phenomenon out of boredom.