"I think they did do this at the RNC critical mass. Can anyone corroborate?"

They've done this a few times at Critical Mass rides in NYC. The first time was the RNC ride. They typically wait until the majority of the group has passed, then they annex a small bit at the end, pull the net (the orange plastic netting used to rope off construction sites) across the street, the wrap up the crowd inside. Doing this, they've managed to pin and arrest a lot of bystanders as well.

In regards to what I said earlier about running from the cops... I'm not saying I would, but I am saying the thought has crossed my mind and it seems like it would be easy. These days though NYC is full of scooter cops. I fully accept that while riding, I often break traffic laws (only stop signs/lights... never one ways) and if I do get stopped, I'd have no problem accepting a ticket. No one to blame but myself and my own impatience.