San Franciscans survive on only three Apple Stores within the city limits - the first (and biggest, busiest) in Union Square, another in the Stonestown Galleria, and the newest on Chestnut in the Marina.
Free WiFi... not to mention geniuses :)
Address: 1 Stockton St, SF
Website: http://www.apple.com/retail/locator/index.html?storename=Apple%20Store&q=San%20Francisco