Theodore P. Seto (Loyola-L.A.) has updated his monthly rankings of the Top 15 Graduate Tax Faculties, as measured by the number of SSRN downloads (through 2/1/07):     

For purposes of Ted’s analysis, a tax professor is initially defined as any law professor at a U.S. law school (1) self-identifying with one of the tax categories in the 2006-2007 AALS faculty listing, (2) who has posted at least one tax or tax-related article in abstract or full text on SSRN. Paul Caron’s listing of 2006-2007 new hires and lateral transfers is also reflected. Further corrections are also made as requested. As is true of Paul Caron’s ranking of individual tax professors, downloads of all SSRN postings of any tax professor, so defined, are then tallied.

For more on the use of SSRN downloads in law school rankings, see Bernard S. Black & Paul L. Caron, Ranking Law Schools: Using SSRN to Measure Scholarly Performance, 81 Ind. L.J. 83 (2006).