The wine is ridiculously overpriced here and not that great. Stick to local beers.
On the other hand, weed in the US is much better than what you're used to in Argentina. Take it easy with it, though. It's also much more potent.
The social scene in SF, while not NY or LA, is pretty good, and huge compared to what's happening on the peninsula. If I were single I wouldn't want to live on the peninsula. Once you have a gf, it might be cool. It's a bit suburban for me. By the way, making out in public and other public displays of affection are mostly taboo. Californians are laid back and not much bothers them, but people are still a bit uptight in that regard. Go figure.
Good luck finding yerba. Some of the latino supermarkets must carry it.
The steak will be a major disappointment. Just forget about it. Otherwise the food's fantastic. You have a lot more options than you do in, say, BsAs, even on the peninsula. People eat dinner super early. 8 o'clock is normal. You're pretty much expected to tip at least 15%, unless the waiter really screws something up. There are tip jars everywhere. Ignore them if you're not a regular. Otherwise, you're kind of obligated. You will not believe the tipping.
If you live in SF you don't need a car. If you live in Mt. View it's going to be harder to get by without one, but keep in mind that, in California, bicycling is socially acceptable, and a cheap and effective means of transportation. The climate permits cycling year-round. I did it for a year in Palo Alto. Don't take cabs in SF unless you can share one or it's some kind of emergency. They're ridiculously expensive, and mostly serve rich people and tourists. If you do take a cab, you're expected to tip 15% on top of the already-ridiculous fare. Caltrain is a fine way to get up and down the peninsula, though here in yanquilandia you're not allowed to hang off the side. Dumb rule.
Suerte.