Thomas Ricker, writing for The Verge:
I consider "tourist" to be the filthiest of words. It's the curse I grumble when caught behind pedestrians walking without purpose on big-city sidewalks. But I differentiate between explorer and tourist: the former being someone that travels to an unfamiliar place to learn about it, the latter a barbaric asshat driven by the desire to document his very existence. The "I was here" photographer with a penchant for flashing a peace sign. I've lived here in the Bay Area my entire life, but only have I lived in San Francisco a few months. In that time, though, I feel like I've gotten to know a lot about the city as if I were a native San Franciscan. I'm even able to tell a tourist from a local, for the most part. My girlfriend and her mom have worked a lot to acclimate me to the city, and I feel like I've acquired a lot of knowledge in a short period of time. I'm comfortable with navigating our Richmond neighborhood on my own, as well as taking the bus through Golden Gate Park and to downtown.
Speaking of the bus, SF Gate has a nice slideshow on the best Muni routes for seeing San Francisco. I've been on a few of these lines, and have seen most of them around town. Paying $2 to tour the city via public transit sure beats paying more for a ticket on those ginormous tour buses that are all over the place.