Yes, Flash Mob videos have become dime a dozen, but I'd like to recommend heartily this one from a Brno shopping center.
It comes from bicontinental friend Charlie Cockey, a San Franciscan film-maven active in Europe (and at San Jose's upcoming Cinequest), who makes his home in Brno for most of the year. He writes:
Our own hometown Flash Mob, in the downtown Vanková Shopping Center, where the Modern and Experimental Music Festival used to be held, I met Louis Andriessen there when he was a guest for the local performance of his amazing piece De Staat.This surprise concert is by the Brno Symphony, playing Smetana's Vltava (The Moldau) from Ma vlast (My Homeland), probably the single most known piece of classical music here ever since its 1882 premiere in Prague.