Yeah, we do the critical mass thing. It's a lot of crusty punk types mixed with the kind of random sample you get from the cycling community. The numbers go way down in the winter. The cops have come in and clubbed people once or twice, fyi.
There is also a midnight riders group, and on big american holiday weekends (labor day etc.) about a hundred people ride, which is a lot for this city. Quite fun. Again, cops have attacked in rare circumstances.