Marisa L. Ramirez et al. have published "Do Open Access Electronic Theses and Dissertations Diminish Publishing Opportunities in the Social Sciences and Humanities? Findings from a 2011 Survey of Academic Publishers" in the latest issue of College & Research Libraries.
Here's an excerpt:
An increasing number of higher education institutions worldwide are requiring submission of electronic theses and dissertations (ETDs) by graduate students and are subsequently providing open access to these works in online repositories. Faculty advisors and graduate students are concerned that such unfettered access to their work could diminish future publishing opportunities. This study investigated social sciences, arts, and humanities journal editors' and university press directors' attitudes toward ETDs. The findings indicate that manuscripts that are revisions of openly accessible ETDs are always welcome for submission or considered on a case-by-case basis by 82.8 percent of journal editors and 53.7 percent of university press directors polled.