Ecstatic Dance - San Francisco
Ecstatic dance in San Francisco is delightful. They have these dance events every Sunday morning (~11am-1pm) at the Church Of 8 Wheels (near Alamo Square/Hayes Valley), and if you get earlier you might get yoga or a contact improv lesson (on the 1st Sunday each month).
What is Ecstatic Dance
I think the best thing you can do, for a full explanation, is to read my Ecstatic Dance article. It explains things in depth. In a nutshell: wonderful tribal music where you are free to dance however you want (no instructions) and no shoes. In the dance, the only real rule is to be respectful to others and no photos. Remember that putting your hands together in a pray like position is saying "thanks, but I want to dance by myself now".
The San Francisco Venue
San Francisco (SF) Ecstatic Dance is a fairly young crowd in a beautiful old church where they usually have roller skating. Lots of people seem to want to dance in their own space, but if you want to dance with others, you might be lucky to make eye contact and have a great dance. :)
I like that they have water off to the side... there are only two toilet stalls though (one for each gender), so you probably want to change before getting to dance.