One specific incident involves a T-Mobile ad, featuring people dancing at the Liverpool Street Station in London.
After watching the ad on TV, a Facebook member created the group "Liverpool Street Station Silent Dance” to organize something similar for friends. The group grew virally as friends invited their friends, and so on. An event was made, and when it occured it was enormous and filled with great energy. The amount of people at the station was so large that it closed down the station.
With this incident, it is interesting to compare it to the one mentioned by Niedzviecki's article "Facebook in a Crowd." In both incidents, random people were invited to attend. However, in Niedzviecki's event barely anyone showed up. It brings up the question of why the Londan flashmob event was so much more successful.