Close to the Powell St BART station. See http://www.bluebottlecoffee.com/cafes/mint-plaza .
Meetup.com's location picker thingy doesn't seem to quite be sure where this is, because it didn't supply me an address when I typed in the name. According to Google, Mint Plaza is not the same as Mint St: http://goo.gl/maps/V7mbR
To be fair, I haven't been here ... it just looked interesting! If anyone has cautions against it, I'm certainly willing to change venues.