In our article, Ranking Law Schools: Using SSRN to Measure Scholarly Performance, 81 Ind. L.J. 83, 93 (2006), Bernie Black and I note that one of the problems with using citation count rankings is that they favor more senior faculty and value older work that accumulates citations over time.  The Chronicle of Higher Education reports on a new method developed by Northwestern University researchers that measures the speed in which articles accumulate citations, thus mitigating the bias in favor of older faculty and older articles.  The article is in PLoS ONE:  Effectiveness of Journal Ranking Schemes as a Tool for Locating Information, by Michael J. Stringer, Marta Sales-Pardo & Luís A. Nunes Amara.