The Social Science Research Network (SSRN) is a vast repository of working papers in the Social Sciences. At present, they have downloadable versions of over 93,000 working papers (with abstracts of another 30,000) by over 62,000 unique authors, and they receiving new pieces at the rate of about 30,000 per year. I'd argue that SSRN is one of the most significant developments in the way academic research is conducted and disseminated (at least in my field) in the last decade or so.
Statistics on the number of times an individual's papers from SSRN have been downloaded are rapidly becoming an additional measure of the scholarly impact of their work. In addition, it's now common for academics to list the URL where there SSRN papers can be downloaded.
Matt Bodie at PrawfsBlawg has a very nice interview with Gregg Gordon, the President and CEO of SSRN (and one of its founders in 1994). In it, Gordon gives some of the history of SSRN, talks about some of the ways SSRN maintains the integrity of its download statistics, and hints at some of SSRN's plans for the future.
Read the whole thing here.