This from Charles Bailey's excellent 'Current Cites'
Sale, Arthur. "The Acquisition of Open Access Research Articles" University of Tasmania EPrints Repository (2006). - In this e-print, Sale examines what happened when the Department of Electronics and Computer Science at the University of Southampton, the Queensland University of Technology, and the School of Computing at the University of Tasmania mandated the deposit of article e-prints. Based on an analysis of the deposit data at these academic units, Sale concludes: "What can be estimated is that a university-wide mandatory deposit policy takes at least three years to be (say) 80% effective, if it is the authors themselves who provide their documents. If the repository managers adopt a proactive policy of actively uploading missing documents on behalf of the authors, as at CERN http://public.web.cern.ch/ then the apparent transition will be faster, but the rise of self-archiving might be slowed due to lack of direct author incentive and involvement. Repository managerial promotion and assistance, such as that undertaken by the Library in QUT, matters very significantly under a mandatory policy, although under voluntary policies it seems to be largely a waste of money. . ." - CB