That is so cool....!!
I think it's even better then my former favourite Hammer Pants Dance.
I've always been fascinated of the flash-mobbing I've never participated in any thou, I miss the only that I know of in Aalborg. Maybe I should see if I can find something about flash-mobbing in Monterrey before I go there?
EDIT
I love this as well: Frozen Grand Central
And this is also very cool: The T-Mobile Dance maybe especially because you can see the rehearsals: T-Mobile Dance Rehearsals
I know that some of these are commercial but still... :-)