[Disclosure: I've been a supporter of the Harvard initiative since its inception and have provided informal input to its proponents periodically along the way.]
How big a deal is this initiative by the Harvard Faculty of Arts and Sciences? It's huge.
First, this is a bottom-up initiative. Open access advocates have been working hard over the years to get faculty authors to pay greater attention to their copyrights. While faculties at various institutions have adopted resolutions supporting open access as a principle and as a goal, this is the first time that faculty authors as a group have stepped up and really acknowledged that the Internet matters and that business-as-usual publishing fails to take advantage of the Internet as a means for spreading knowledge throughout the world.
Second, by precommitting themselves in this fashion, the faculty has recognized that copyright is an author's right. With rights come responsibilities. These authors have committed to each other that they will take greater responsibility for managing their copyrights and for providing the public with free access to their work.
There are a number of heroes in this story. Within the administration, Steve Hyman, the provost, set up a faculty committee to study scholarly communication issues and practices. Stuart Shieber (Computer Science) chaired that committee and, along with his committee members, labored for more than a year to make this happen.
It is now up to faculty on other campuses to reflect on whether they too are willing to be responsible authors in the twenty-first century.