"According to U.S. Census Bureau data, in 2008, blacks and Hispanics constituted only 1.5% and 4.7% respectively of the Valley’s tech population —well below national tech-population averages of 7.1% and 5.3%. You hardly find any blacks in positions of leadership in Silicon Valley companies. There is at least an unconscious bias."
Related: Douglas Hofstadter's satirical article on exactly that topic, which you reminded me of and which I'm glad I could remember enough of to find: http://www.cs.virginia.edu/~evans/cs655/readings/purity.html