Here are thoughtful comments on OA from Peter Suber, Director of the Harvard Office for Scholarly Communication (OSC), Director of the Harvard Open Access Project (HOAP), a Faculty Fellow at the Berkman Center for Internet & Society, and Senior Researcher at the Scholarly Publishing and Academic Resources Coalition (SPARC):

http://lj.libraryjournal.com/2015/09/opinion/not-dead-yet/an-interview-with-peter-suber-on-open-access-not-dead-yet/#_

And here is a recent article on a study of the use of Subject Repositories:

“The Role of arXiv, RePEc, SSRN and PMC in Formal Scholarly Communication”  (DigitalKoans)

Xuemei Li has self-archived “The Role of arXiv, RePEc, SSRN and PMC in Formal Scholarly Communication.”

Here’s an excerpt:

The four major Subject Repositories (SRs), arXiv, Research Papers in Economics (RePEc), Social Science Research Network (SSRN) and PubMed Central (PMC), are all important within their disciplines but no previous study has systematically compared how often they are cited in academic publications. In response, this article reports an analysis of citations to SRs from Scopus publications, 2000 to 2013.