That goes way beyond "corking" - that is deliberately stopping traffic on a busy road at a busy time of day for the express point of pissing off as many people as possible. Our Critical Mass ride is completely different. We keep to one lane, always leaving a lane free for cars to get by, we are friendly, we stop at red lights and we ride well past rush hour when traffic is light. The only "corking" we do is to stop cars long enough for the group to get through a light. We treat the group of cyclists as though it were a single bus or 18-wheeler and move as one unit. If the light is red when we get there, we stop. If it turns red while we are going through, we get everyone through. Its fun, and the motorists seem to enjoy it too. We even bring the kids along.
something about flies and honey and vinegar...