The July 18 issue of Science has an interesting article titled Electronic Publication and the Narrowing of Science and Scholarship, by James A. Evans, a sociologist at the University of Chicago (Science 18 July 2008: Vol. 321. no. 5887, pp. 395 - 399 DOI: 10.1126/science.1150473).
I've seen research or statistics (note to self - go dig them up) that indicate materials placed in institutional repositories are cited far more often than articles that are only available in print, and that seems to make sense since they're quickly and easily located via the web.
But Evans's research seems to suggest something to the opposite effect. His conclusion (and I have to admit I have to take his word as most of the methodology goes over my head) is that (italics mine),
"electronically available journals may portend an ironic change for science... I show that as more journal issues came online, the articles referenced tended to be more recent, fewer journals and articles were cited, and more of those citations were to fewer journals and articles. The forced browsing of print archives may have stretched scientists and scholars to anchor findings deeply into past and present scholarship. Searching online is more efficient and following hyperlinks quickly puts researchers in touch with prevailing opinion, but this may accelerate consensus and narrow the range of findings and ideas built upon."
Very interesting, and quite important as we continue to move towards digital-preferred collections. Now of course he isn't looking at the quality of the research. Maybe these newer articles citing fewer resources are actually tighter and better than their predecessors?