Last Thursday at 11:00 there was an excellent example of the flash mob form in Liverpool Street train station in London where most of the concourse starting dancing.  I am calling it an "example of the form" because it was actually organised by T-Mobile, but aside from that it had all the hallmarks: A group of people who turn up, do something, melt away afterwards, and most important of all; the general public knows nothing about it.

The whole thing was captured on 10 cameras (hidden in sports bags and the like) and was then broadcast on TV the next night.

I imagine that people will start arguing about whether it "real" or "fake" because a corporate organised it in the first place.  Personally, I think the event was cool and that any such argument is missing the point.

Check it out.