The reason I flew to San Francisco was to renew my Indian visa. When I decided to go back to India, I didn't think there would be enough time to do it by mail, and it costs a lot to have things Fed-Exed to and from my island. My roomie (N.) just recently moved back to SF, and the flights to India are cheaper from the mainland than from the island, so I booked a flight to India from SF, and flew over a week earlier, to get the visa and see N.
It is pretty easy to do the drop off thing. You make an appointment online as you are filling out the application, and they check that you do have one before they let you in. You had to have all your documents and either a money order or exact cash in a plastic bag or a manila envelope. (You are not allowed to bring anything into the office except that.) They confirm that you have all paperwork, take your money and give you a receipt to bring back at the end of the day.
I spent the day playing tourist (riding the cable car, browsing City Lights bookstore, people-watching), and at 5.30, went back to the visa place. The courier brings everything back from the Indian embassy at 5.30, and once they get it all organized, they take your receipt and give you the passport with the visa in it. There was a long line of people waiting and a few were disappointed as their passports didn't come back, and they will have to come back Monday at 5.30. My flight is Tuesday so I was a tad worried. What a relief to have it in my hands!