How can the funders of research and the researchers themselves prove that the results of their work are publicly available and more, that they are being used?
Altmetrics could be the answer. Not sure what Altmetrics is? This paper from the Australian Open Access Support Group provides a brief and succinct summary: http://aoasg.org.au/2013/05/23/altmetrics-and-open-access-a-measure-of-public-interest/