Well, two months ago I noticed a piece at Blunted on Reality about a study done by Northwestern U. noting how people interpreted facial expressions of black people more negatively than they would the same facial expressions on white people. Last month, Geoffrey posted a note linking to the research report (PDF), which has been sitting in my inbox ever since.  If you do choose to read it, it's pretty interesting because first impressions do very much in shaping how you view a person, and if the the decoding of expressions is already slanted against the black person, it makes it that much harder to break through the stereotype. This may also explain why it takes practically a shucking- and-jiving show grin from black people to show the public that "I am not a threat."