Joyce Chapman, Jody DeRidder and Santi Thompson have published "Developing Best Practices in Digital Library Assessment: Year One Update" in D-Lib Magazine.
Here's an excerpt:
In the face of limited resources and increasing demand for online access to digital library content, we need to strategically focus our efforts and better understand users, impact, and associated costs. However, methods for assessment of digital libraries are not standardized. In an effort to address this crucial gap, the Digital Library Federation Assessment Interest Group has engaged the community over the past year in the development of best practices and guidelines. With this article, the authors provide an update on progress to date and solicit participation in an evolving effort to develop viable solutions.