Public transportation in S.F. is great if you have a lot of time on your hands. So it may be perfect for some people's vacations. The bus system is widely criticized for a lack of reliability and a lack of capacity.
Buses go almost everywhere, they just come unpredictably and in an unscheduled manner.
An empty bus is a lot of fun to ride in, but most buses are VERY full. You can use the BART trains to visit outlying suburban areas after you have had your fill of S.F. city life. BART Subway Trains - Electronic Gating System BART takes you long distances from the city to the suburbs. It's best for reaching the East Bay including Berkeley. But the stops are very limited and it usually requires a link with other buses.