SD15 Hit or Miss portraits!

Do any other SD users find that when using the your SDxx for Portraits there are constant autofocus issues and quirky metering issues? But when using it for macro shots or inanimate objects it works like a charm. Mine doesn't like to lock on to peoples faces. The problem happens with all my lenses (six of them) and the entire set up has been sent in for calibration multiple times. It seems like when I focus on a flower or a insect the AF locks right on and the exposure is right on too. Too bad flowers, landscapes and insects don't pay to have their image taken...