San Francisco has meters which go dormant at night, and appear to be non-function if you were to pull up to the meter and park before meter enforcement hours. They will NOT permit you to feed money in advance of enforcement hours, they will simply wake up at the designated time and start to blink 'Violation' until you come back to feed the meter or the parking enforcement arrives and starts writing tickets. That is what I experienced last year, and I was lucky in needing something out of my car, which brought me back two minutes after the meter woke up! However, according to SF official web site, you can now prepay meters for the time you need even if you arrive before the meter begins to be enforced you will not be charged until the meter begins operation (e.g., at 9 a.m.). Prepayment begins at 4:30 a.m. at all meters every day (except at Port meters near waterfront). (Watch out, I don't know if what the web says is in full implementation! Better safe than sorry.)
San Francisco has meters which are variable in parking fee rates, based upon demand. Most meter rates are between $2.00 and $3.50 per hour for cars, and city has piloted demand-responsive pricing in SFpark pilot areas, where rates incrementally adjust every 6-8 weeks based on demand and may range from $0.25 to $6.00 per hour.
As of January 2013, parking meters are in effect all days of the week, including Sundays.
Watch out for street cleaning signs on which one side of the street cannot have any parking on a certain period for street sweeping...your car WILL be ticketed, the cops precede the street sweepers since it helps reduce the city's income shortfalls!
Most neighborhoods that are near key routes for mass transit use officially issued neighborhood stickers so that residents can park all day, while other cars are rigidly enforced for 2 hour limit, so that commuters do not take up all the parking all day and prevent residents from parking.