I've seen them with my own eyes. But you'll find they are extremely willing and will usually go out of their way to be helpful. Microfilmed years start with 1861. The films are in drawers on the back side of the very last row of cabinets. The San Francisco Main Library has them starting with 1953, all in print, on the fifth floor, by the newspaper desk.
Books are on the shelves all the way in the back, past the computers.
Please use these with the utmost care. The staff is very good about showing you how to use the readers and copiers if you aren't familiar with how they operate. Sutro Library Microfilm collection contains most years between 1861 to 1935. Extensive collection in book form as well, of both City Directories and Telephone Directories. Sutro has City Directories in book form, microfilm and microfiche for cities and towns all over the country.