If you want to take sailing lessons or charter a sailboat on San Francisco Bay, I'd recommend Modern Sailing Academy. Yes, the name's awkward. Some of the boats are older, but it's mostly good stock. The staff is friendly and helpful.
Don't get sucked in by all those new Hunters over at Club Nautique. They look nice, but sail like crap. We walk the Nautique boats all the time, and the staff is rude and boorish.
Chartering from Sausalito is great. You have a few minutes of motoring to get the boat set up and settle the crew. You can unfurl with plenty of sea room just past the Spinnaker restaurant (white gravel roof on the point), and reach up to the Golden Gate bridge quickly. And you'll know if you need a reef before you leave the dock!