Ulrich Herb has self-archived "OpenAccess Statistics: Alternative Impact Measures for Open Access Documents? An Examination How to Generate Interoperable Usage Information from Distributed Open Access Services" in E-LIS.
Here's an excerpt:
Publishing and bibliometric indicators are of utmost relevance for scientists and research institutions as the impact or importance of a publication (or even of a scientist or an institution) is mostly regarded to be equivalent to a citation-based indicator, e.g. in form of the Journal Impact Factor or the Hirsch-Index. Both on an individual and an institutional level performance measurement depends strongly on these impact scores. This contribution shows that most common methods to assess the impact of scientific publications often discriminate Open Access publications — and by that reduce the attractiveness of Open Access for scientists. Assuming that the motivation to use Open Access publishing services (e.g. a journal or a repository) would increase if these services would convey some sort of reputation or impact to the scientists, alternative models of impact are discussed. Prevailing research results indicate that alternative metrics based on usage information of electronic documents are suitable to complement or to relativize citation-based indicators. Furthermore an insight into the project OpenAccess-Statistics OA-S is given. OA-S implemented an infrastructure to collect document-related usage information from distributed Open Access Repositories in an aggregator service in order to generate interoperable document access information according to three standards (COUNTER, LogEc and IFABC). The service also guarantees the deduplication of users and identical documents on different servers. In a second phase it is not only planned to implement added services like recommender features, but also to evaluate alternative impact metrics based on usage patterns of electronic documents.