Public transit in SF works well in some areas, not so well in others -- even making a single connection can add 30 - 45 minutes to your commute If you're going to the financial district or north SOMA, transit is usually viable, if you're going anywhere else, it's likely not so viable.

And this is a city that's only 7 miles wide -- I used to be able to bike downtown in less than than I spent waiting on the bus on most days (since I didn't just have to wait for one bus, I had to wait for a bus that wasn't already full to take on passengers)