"The coolest thing ever!"

I've had this saved in my Twitter favourites since the middle of last year (thank you, @JillMansell!). I just watched it and it blew me away. Apart from the fact that it made me sob, as flashmobs always do, it just looks completely gorgeous and I can't imagine how much time it took to organise.

Also? I didn't know this song was by the Black Eyed Peas. My publishers are right about me: I really do have my finger on the pulse. Ahem.

I would love to be part of a flashmob, but I don't know what I'd like to do. Any ideas? If you were going to join a flashmob, what would you want to do?