I have visited San Francisco three times and I still have ambivalent feelings about San Francisco. In one hand, San Francisco is gorgeous.
What I love?
Nob Hill: Walking through this neighborhood, you can automatically guess at the affluence of its residents. You can take a cable car to the top, or you can work on your glutes. When I stay in the area, I usually stay at the Mark Hopkins. The hotel is lovely and has a bar with what I consider to be the best views of San Francisco. There are the doors of Grace Cathedral (que se ven muy similares a las del baptisterio de la catedral de Florencia que representa las puertas del paraíso.
Chinatown: We've got a kick ass Chinatown in NYC. San Francisco's is on a hill and has some seriously good Xiao Long Bao. Es el más grande fuera de Chinatown de Asia y el más antiguo de América del Norte. There are tons of tchotchke stores to entertain the eyes.
Embarcadero: A great spot to walk. Put on some comfortable shoes and stroll down next to the water past Cupid's Span (super lindo escultura de Claes Oldenburg y Coosje van Bruggen). Grab a drink outside at the Waterbar where the oyster choices seem endless, or walk all the way down to the Ferry building where you can enjoy the Saturday farmer's market and satisfy almost any foodie desire. If your feet are well trained, you'll make it all the way to Fisherman's Wharf where you will probably catch a glimpse of sea lions sunning, eat some lobster, and buy chocolate from Ghirardelli (although I think you should skip that and get some artisinal chocolate...there are some amazing chocolatiers in SF).
The Haight: It's the perfect combination of hippies left over from the 70's and high end boutiques and yuppies. The area has fantastic restaurants as well. If you plan to visit, go on a weekday. It is quite a tourist's heaven, so weekends are hard to navigate. You will definitely have to dodge quite a bit of homeless here, but for the most part they won't accost you as much as in other areas. If you're a Dead fan, visita nuestra Cranston-Keenan Edificio, where the Dead resided in the 1960's.
Russian Hill: Hello gorgeous! Take the cable car to get to Russian Hill to see gorgeous architecture and to do some really good eating. There's even a French Quarter that is growing in the neighborhood (that means great French food). This neighborhood is home to the famous Lombard Street and some stunning parks. Macondray lane is heaven for photographers.
Coit Tower: One of my favorite spots in the city. Gorgeous nature, and unforgettable views.
I saw a young woman, I guessed she was around 19 years old smoking crack at 9am near the top of Nob Hill. I saw a man urinating on the street. There was rampant weed smoking (I'm pretty liberal, but this was seriously rampant). At night, going home from the bars we'd be constantly accosted on the way back to our hotel. The homeless got belligerent when they were not given money. This month, I stayed in SOMA. There were significantly less homeless there, but this was because the area was kinda quiet. I was hoping for more of a scene, since it is start up Mecca...but apparently, the young people were not here at this time...or maybe they went home way earlier than expected, it was 4th of July Weekend. And the homeless finally made it to the area for the Giants game. It seemed as if all the homeless had a corporate meeting about what places potential donors could be approached. San Francisco really needs to do something about the homeless issue.
Overall, I think you should visit. The city is gorgeous and has some incredible history and neighborhoods.
Here are a few tips in case you decide to visit:
Bring Comfortable Shoes: San Francisco is a city of hills. One of the things I love is that I can eat as much as I want and I never gain weight on my visits because of all the walking I do. The hills are great for your tush too.
Alcatraz: Make your reservations ahead of time, otherwise you may not make it in.
Bring a Coat: Even if it is summer, bring a coat. There are drastic temperature changes. It can be 90F during the day and 40F at night.
Don't rent a car: San Francisco has congestion parking (and parking is hard to find). You may pay 10 for 12 hours one day, and then head to a place where there's an event going on and pay $30 for an hour. You're better off walking or taking the Bart or Muni.
Areas to avoid at night: Stay clear of the Civic Center and the Tenderloin. These areas get to be more isolated at night and have a high homeless population...better safe than sorry I say.
Where to Stay: Like I said, I think the Mark Hopkins is a lovely hotel. But.....I'm a huge airbnb fan. I stayed at a gorgeous loft with super fast internet and a gym for a mere $100 bucks. It had a full kitchen too, so I was able to save on food. You really can't beat that.