Emily Puckett Rodgers and Sarah Barbrow have self-archived "A Look at Altmetrics and Its Growing Significance to Research Libraries" in Deep Blue.
Here's an excerpt:
This document serves as an informational review of the emerging field and practices of alternative metrics or altmetrics. It is intended to be used by librarians and faculty members in research libraries and universities to better understand the trends and challenges associated with altmetrics in higher education. It is also intended to be used by research libraries to offer guidance on how to participate in shaping this emerging field.