In reply to wert:
Mission Cliffs is easy to get to on BART it's a nice wall and very friendly but nothing really special in terms of climbing terrain. More roped climbing than bouldering and more real-life San Francisco than tourist-trap.
Planet Granite is in an awesome location and when I was there had some unusual and fun bouldering features like a top-out boulder and a long ramp between floors with routes set across the roof. There are huge windows looking out to the Golden Gate Bridge.
I went out to Planet Granite in a taxi had a couple of hours climbing and walked back into town along the waterfront past Fisherman's Wharf and cutting up[ through China Town. It's a long walk but a great way to see some of the best bits of San Francisco.
I'm not sure if you can get signed off to lead as a visitor, from memory most of the walls were top roped anyway.