In practice, you get so much accidental diversity between any two intelligent individuals (we are all quite different) that its rare that you have to go looking for more. Diversity is the great good and ideal of our time, but a rather flimsy idea when you get right down to it.
In the context of wanting to write the next Digg, I would propose that a better application of their conclusions would be, e.g., to favor hiring programmers from different schools over hiring programmers who went to the same school and studied under the same professors. In this way you might get some diversity in terms of how your programmers approach solving problems versus having a group of programmers who each approach a given problem in the same way and presumably reach the same conclusions / solutions.
There were blacks, whites, hispanic, men, women, but as I looked over the faces I thought, "Lawyer, lawyer, lawyer, not sure, lawyer, ..." and wondered where, exactly, was the diversity?
Arbitrary or superficial diversity is not a good goal.