Joachim Schöpfel and Hêlêne Prost have self-archived "Altmetrics and Grey Literature: Perspectives and Challenges."
Here's an excerpt:
The topic of our paper is the connection between altmetrics and grey literature. Do altmetrics offer new opportunities for the development and impact of grey literature? In particular, the paper explores how altmetrics could add value to grey literature, in particular how reference managers, repositories, academic search engines and social networks can produce altmetrics of dissertations, reports, conference papers etc. We explore, too, how new altmetric tools incorporate grey literature as source for impact assessment, and if they do. The discussion analyses the potential but also the limits of the actual application of altmetrics to grey literatures and highlights the importance of unique identifiers, above all the DOI.