I have never participated in one of these. From some youtube videos, it seems that there is a tendency in some cases for cyclists to stray toward the left, to not keep right for the sake of faster traffic, and in some shots it appears that motorists are being deliberately blocked. Is this supposed to be a kind of protest? I think the rides are intended to demonstrate the viability and indeed existence of cycling as a mode of transport. I think it would be better if the cyclists were scrupulously following the traffic laws. A long string of cyclists obeying the traffic laws might convince more people and avoid attracting the attention of the police. To behave in a noisy and anarchical way invites legislation etc. In one youtube video the police showed up and handed a list of citations to some cyclists, just to indicate to them how many infractions had been incurred. The cyclists didn't seem to take it very seriously.