Commenter N in Seattle raises an interesting point: should Sotomayor be confirmed, three of the nine members of the Court (Sotomayor, Alito, Thomas) will have attended the Law School of New Haven State University; four (Roberts, Breyer, Kennedy, and Scalia) will be alumni of the Umass-Cambridge School of Law. Note that Yale has one-third the number of studens as Harvard, meaning on a per-alumn basis it's clearly the best breeding ground for Supreme Court justices. Ruth Bader Ginsburg went to SUNY-Harlem (though she started her education at Harvard!), meaning that John Paul Stevens (Northwestern) will remain the only member of the Court who attended law school outside the 223 mile stretch between Harlem and Cambridge. He remains the last justice who attended a law school that was neither (a) in the Ivy League, nor (b) Stanford. The last justice to attend a state school was Warren Burger, nominated in 1969. So while Sotomayor's nomination brings the demographics of the Court closer in line with America's, and her early career path is somewhat atypical of SCOTUS picks, she likely took classes from similar professors and interacted with similar peers while at school. This was another reason to modestly prefer Diane Wood JD UT-Austin '72 over Sotomayor. Can't always get what you want, I guess.
Selection bias tends to be more manifest at extremely high levels of achievement. If American education has only a modest tendency to push women away from math and engineering, MIT will be overwhelmingly male no matter what. Thus one possible reading of the tilt towards super-elite law schools for Supreme Court justices is that there's likely a tilt towards in other top pre-Justice career paths—law professors at top law schools, circuit court Judges, top legal positions in the Executive branch, etc. Since it's unlikely that these schools are the only place one can learn to be an appellate judge or Solicitor General, the Obama Administration might want to consider instituting something similar to the Rooney Rule, so that they at least interview top graduates of great-but-not-outstanding law schools when vacancies arise. Surely some of them would prove capable jurists.