I've seen a few videos of meditation flashmobs -- the problem is that watching one via video is pretty much like watching paint dry. Here is a live report from a Brit who had her doubts but went to see for herself what it was like actually being part of one.
Naseem Khan reflects on her experience in this article -- "Meditating in public places has always made me uneasy, but this flashmob was half an hour of the purest sanity..."
I'm grateful to Naseem for her report -- much more interesting than a video. . .