At 6:17 p.m. on Friday, April 18, 2008, a few thousand kids arrived at Union Square, plugged in to their iPods and rocked out to the beat of their own drums. The Silent Rave, a take-off of a similar event in London, had no agenda. This was simply dancing for the sake of dancing. Missed out? The organizers (type "Silent Rave New York" into Facebook) promise they'll be back in June.