I should have also mentioned Crissy Field. Since the City took over the Presidio, they have also done a great job in making that area a great open space recreational area. If you have not seen it in the last year or two, you should. They have removed the air strip and replaced it with a tidal area/wetlands, but with multi use pathways (bikes/jog/walk).
Business takes me into the city fairly often, otherwise, I would only go there for occasional games (Niner's mostly.