Muni cars run on clean electric lines, and their busses are now electric hybrids. Each is outfitted with a GPS that updates boards at each stop to let you know in real-time how long before the next bus arrives. They have a phone number and a website that has this real-time info too. Hell, that website even has an iPhone version!
It costs 45 bucks a month to go anywhere you want. It runs 24 hours a day with plenty of frequency and services pretty much every inch of the city. What more can you ask for?
Ever checked out Atlanta's MARTA system? The bus service is random and wait times are often 30 minutes to 2 hours. Without a car, you're basically screwed.