When reading about a city on Wikipedia etc, I can never tell how frequent public transport is, and whether it's good outside tourist areas. So thanks whackojacko and _corbett for your views.
511.org will tell you how long it takes to get from place to place in the bay area.
It really depends on the bus line how frequent they come. The 9 and 47 come right by my house and come every 10-15 minutes if not less. They are both heavily travelled lines. The 12 also comes by and it's less travelled and probably averages one bus every 25-30 minutes or so.
There is also a bus schedule that they "try" to adhere too. That's true for almost every city, so you can just look at the lines that run by where you are going to be and see how often they come.
Finally, all of the SF MUNI Buses and trains are gps equipped so you can check a pretty accurate estimate of when they will be at your stop online or through various smartphone apps. Very handy for preventing you from having to wait at a bus stop for more than a few minutes.
