Lee Epstein, one of the nation's leading political scientists engaged in empirical study of the courts, and her partner Nancy Staudt (tax), both professors at Washington University, St. Louis (Epstein in political science and law, and Staudt in law) have accepted senior offers from the law school at Northwestern University. These appointments pretty clearly solidify Northwestern's status as one of the two or three leading centers for empirical, social scientific study of the legal system in the United States.
UPDATE: One reader asked what the other leading centers were, which is a fair question. Certainly Cornell has to be up there, and perhaps in terms of total numbers of faculty doing recognized work in these areas, Northwestern and Cornell lead everyone else. But there are notable clusters of folks doing this kind of empirical work at lots of other top law schools.