Brian D. Edgar and John Willinsky have self-archived "A Survey of the Scholarly Journals Using Open Journal Systems" on the Public Knowledge Project website.
Here's an excerpt:
A survey of 998 scholarly journals that use Open Journal Systems (OJS), an open source journal software platform, captures the characteristics of an emerging class of scholar-publisher open access journals (with some representation from more traditional scholarly society and print-based titles). The journals in the sample follow traditional norms for peer-reviewing, acceptance rates, and disciplinary focus, but are distinguished by the number that offer open access to their content, the growth rates in new titles, the participation rates from developing countries, and the extremely low operating budgets. The survey also documents the limited degree to which open source software can alter a field of communication, as OJS appears to have created a third path, dedicated to maximizing access to research and scholarship, as an alternative to traditional scholarly society and commercial publishing routes.