FWIW, a group here in So Cal (the San Fernando Valley, to be exact) has been doing this for a couple years It was featured in Hot Rod Magazine about one year ago. And yesterday morning or earlier today, apparently one of the riders was killed when he smacked a parked SUV. Tore his helmet off, etc. I haven't seen the actual news story...just heard it briefly on the TV this morning when I was getting dressed. Been too busy today to look it up, but I'm sure it's out there. Apparently the organizer(s) may be cited with some kind of misdimeanor for unlawful assembly or illegal use of a non-motorized vehicle or something, but no felonies. Sad.
-Dean in So Cal