Here is a very interesting article on a study done by two economist.
The basic conclusion, not surprising in my opinion, is that there is a racial bias: black players get called for more fouls than white players when the referees are white. The opposite is true but the numbers are weaker (white players/black officials).
Please don't make this into an inflammatory thread by saying stupid things like "well the black players in the nba are more violent like stephen jackson" type of thing. Nonetheless, I am interested in hearing people's reactions. I am sure our white brother Hinrich would be surprised considering all the fouls he gets called for. Interestingly enough the NBA did a counterstudy and guess what...there was no racial bias in their study which was a much less formal and detailed study than the one by the academics.