I rode Butter Lap on Wednesday w/ Margo (most of the way)– it was fun. There were probably 20-30 people on the ride, almost all strangers.
People meet at 7pm at the Ferry Building every Wednesday and ride a set route, ending in the Mission for a beer (usually at Bender’s). This has been going on every week for many years– I’m not sure if there’s even an organizer/owner any more.
[edit: see also the more recent Butterlap debrief for a better map than I’d had here]