From the 2nd May the NIH is requesting that NIH funded investigators submit an electronic copy of the final form of a manuscript for inclusion in PubMed Central. A period of 12 months is allowed, although a more rapid submission to PMC is encouraged. How is this affecting journals? Some journals are publishing editorials about this: today I have seen the NEJM and the American Journal of Respiratory and Critical Care Medicine's responses.
NEJM (this editorial is free)