Great city, but overrun with homelessness.
I enjoy going to San Francisco, and I usually stay downtown near Union Square. You can usually use public transportation to get just about anywhere. There are lots of restaurants in the area. What is disturbing is the amount of homeless people wondering the streets, even occupying a whole block in some places. I live in Los Angeles and we definitely have homeless people, but SF seems to have an overabundance which is very sad.
Insider Tip:One of my favorite places downtown is The Old Siam Restaurant - very good food and excellent prices. Be aware of your surroundings. Try not to go to the Tenderloin area. Definitely go to the San Francisco Carnaval which is held every Memorial Day Weekend in the Mission District. Be aware of SF's weather. It is usually very cool, if not cold and windy.