The top four, not surprisingly, are Yale, Chicago, Harvard, and Stanford. I'm pleased to report that George Mason, home of Conspirators Bernstein, Somin, and Zywicki, is ranked number 21 by mean citation count, and 24 by median citation count.
Citation counts, as Leiter discusses, are a rather imperfect measure of scholarly prowess, but the results of the study do comport more or less with what an informed observer would expect, and far more so than U.S. News's "academic reputation" stats. One thing Leiter could do to improve his study is eliminate assistant professors from it. George Mason, for example, has seven assistant professors (an unusually high percentage of the faculty, I think), most of who have started teaching in the last two years. It doesn't make much sense to me to include such newbies in a study of citation counts since 2000.