case study for your reference: using 1d, under flourescent lighting at home, i take the same pix twice under different WB setting and load them onto computer, view via a calibrated CRT monitor, and somehow personally find that AWB is more "accurate" than flourescent WB (less greenish) . and under indoor s orangy lighting, AWB will retain the orangy look, but tungsten WB will make it look rather bluish. but usually i simply use AWB and when it comes to post processing, i wil just adjust the colour temp to warmer or cooler, depending on how i want the final pix to look like
white card is to place it in the lighting for that shot, take a shot of it, then use its information to dail it in as the referece point of the camera's custom WB