Starbucks is ubiquitous in San Francisco, but you'd be hard-pressed to find one in the Mission, Bernal Heights, the Excelsior — the only two Mission stores are technically in Potrero Hill.
Starbucks announced a program on April 8, 2008 that if you get a Starbucks Card and register it online, that when you use that card at their full sized-stores (not licensed stores, such as those in Safeway), you will earn points towards free refills on brewed coffee, free milk options (i.e. soy milk), free syrup modifications (i.e. different flavors of syrup), and a free tall beverage with any whole bean purchase. Please see their website for more details and to register your Starbucks Card. http://www.starbucks.com
Also, at random, Starbucks may send you an email and notify you that they have added an extra $5 on to your card for being a loyal member. The free $5 reward is chosen by computer and is completely random.
Unlimited free WiFi is now offered as of July 1, 2010. You no longer need to make a purchase or have a Starbucks card.