Researchers who are faculty, too, are soon likely to see a clear benefit to them of open access: the ease of creating a list of reserve readings for students.
When materials are open access, all that one needs to do is to note the citation and add a link. No authentication needed, no copyright permissions. If you're planning to use an article or book chapter year after year - or it is clear that others would and should read the items - it is worthwhile contacting the author to inquire about making a copy open access, and it is worth the author's time to make this happen.
This hit home today when I did a search of the Canadian Association of Research Libraries (CARL) Metadata Harvester and came up with a list of search results that looked a lot like the reserves list for a course at the library where I used to work.
It was not unusual for professors to put copies of their own work on reserve, to make sure they were accessible to students, whether the library could afford to subscribe to or purchase the content or not - clearly, a desire to open up access even in the print world.
If I am seeing this, I think we are close to the point in time when others will begin to see it, too. Once we begin to see what those institutional repositories can do, it will become much easier to recruit content.
Added May 16: see also Klaus Graf's 2005 blogpost on Archivalia called Electronic Reserves and Open Access. Klaus asks: Can administrators of Electronic Reserves (ERs) and staff using them in order to support Open Access (OA)? and concludes: Administrators and staff of ERs should support OA by asking for permission to make OA versions of ER materials available. Klaus Graf's post is in the public domain.