The EU-funded project PEER (Publishing and the Ecology of European Research) analyses the scholarly publication process with a focus the impact of repositories on journal publishing.
The final report, which is now available (http://www.peerproject.eu/reports/) states the importance of the right publication strategy:
“Today, the distinctions between the three [scholarly research publication] models (subscription based, OA or repositories) are blurred, although it is becoming clear that the success of OA journals and repositories – as is the case for subscription based journals – depends on the strategies of individual players, and not merely OA status. The success of BioMed Central and PLoS proves that OA status does not equate in principle to lower quality of research as was suggested initially by some concerned authors. At the same time, OA status does not in itself automatically lead to higher citation and visibility for the authors. In the case of repositories, while some (such as REPEC and ArXiv) succeeded in becoming a starting point and not just a destination in scholarly search (i.e. a site actively searched for and not referred to via a keyword based search), many other repositories are less visible.”