I just visited family in San Fran two months ago. I had the same intentions as you. I would HIGHLY recommend you take the 1 hour trip north to Russian River Brewing (Santa Rosa). It was more than worth it. I had simply planned on finding a bottle of Pliny to try from a liquor store, but I couldn't find it and everyone kept telling me how awesome it was. So I went. They don't have a tour but it was so awesome. I had their sampler:
Quite a few of their beers are only sold there.
Also, while on your way back you could try Marin Brewing. Everything there was fantastic also. Especially the IPA.