As readers of this blog know, citation counts are one of the four methods used to rank law faculty scholarly performance (along with reputation surveys, publication counts, and SSRN download counts). (We discuss all four methodologies in our recent article, Ranking Law Schools: Using SSRN to Measure Scholarly Performance, 81 Ind. L.J. 83 (2006).)
Brian Leiter's citation count studies of individual professors by specialties and of law faculties dominate this field, although prior work by Ted Eisenberg and Martin Wells (Rankings and Explaining the Scholarly Impact of Law Schools, 27 J. Legal Stud. 373 (1998)), also is important. For a critique of using citation counts to measure scholarly performance of faculty, see here.
SSRN has now entered the citation count field with its new "References & Cites" feature. For more details, see TaxProf Blog.