Harvard's corporate law blog reports that:
Statistics released publicly by the Social Science Research Network (SSRN) indicate that, as was the case for each of the six preceding years, Professor Lucian Bebchukled SSRN citation rankings at the end of 2013. As of the end of December 2013, Bebchuk ranked first among all law school professors in all fields both in terms of the total number of citations to his work and in terms of the total number of downloads of his work on SSRN.
Bebchuk’s papers (available on his SSRN page here) have attracted a total of more than 4,000 citations.
FWIW, I'm ranked 6th by all-time downloads and 43rd by all-time citations.