Lived here all my life, and even on the Peninsula, nobody has A/C. In the city itself, it's completely unnecessary. Even the hottest day in SF finish off with cooler evenings.

Not having AC in the hotel is not a problem because it is pleasantly cool at night. However, we were there in September during a "heat wave" or so they called it, and I remember being quite uncomfortable when walking outdoors in direct sunlight for long periods of time. I think it was low 90's. And I'm from AZ so I'm no wimp when it comes to the heat. So I just wanted to say that if you pack the wrong clothes based on everyone's comments that it will be cold during the summer time, you may be unhappy. Don't pack for cold OR hot weather, just pack lots of layers, lots and lots of layers. You'll be much happier!