I just recently heard about “Butter Lap”, a laid-back 17-mile ride every Wednesday evening, ending with a beer at Bender’s, Zeitgeist, or so on. I have other plans this Wednesday, but I plan to check it out in the next few weeks. It sounds like it kicks off from the Ferry Building at 7pm.
Map: http://www.mapmyride.com/ride/united-states/ca/san+francisco/836271138504
Bike blog mentioning it: http://bikesandthecity.blogspot.com/2009/06/butter-june-it.html