Michael Illegal drugs are indeed prohibited in San Francisco just like in Germany, but the consumption of marijuana is practiced so openly that one might think it was legal. For example, I recently met our former neighbor on the street, chatted with him a bit, until I noticed that he was smoking a marijuana cigarette! Or when we open one of our windows, it's not uncommon for suspiciously smelling smoke to waft in. Or recently, when I was driving our car on Divisadero Street and had to stop at a traffic light, clouds of smoke even drifted in from the side window of the car next to me! Outrageous!
People don't even have to buy drugs illegally on the street; those who have chronic pain (or can simulate it well) and can persuade a doctor to issue a corresponding prescription are allowed to shop in the public drug store. There, not only are pre-rolled joints available, as shown in illustration 2, but also a variety of other otherwise illegal herbs and the corresponding consumption accessories.
The Wikipedia entry on Medical Marihuana" explains the regulations regarding this legal form of drug consumption. But as everyone watching the TV series "Weeds" knows, applicants end up in a government database. If you later run for president, someone will surely pull out the file and wave it around, so be careful!