Seems like right now all that is there is PLoS Currents (not that that is a bad thing --- I love PLoS Currents). Apparently more will be coming. From their website:
About Rapid Research Notes
The National Center for Biotechnology Information (NCBI), a division of the National Library of Medicine (NLM) at NIH, is a national resource for molecular biology information and as such has a mandate to develop new products and services to meet the needs of the biomedical research community. Upon the recommendation of public advisors, NCBI developed an archival service to support research shared through new venues for rapid communication enabled by the internet. Introduced in August 2009, the archive, called Rapid Research Notes (RRN), allows users to access and cite research that is provided through participating publisher programs designed for immediate communication.
The RRN archive was prompted in part by the spring 2009 worldwide outbreak of H1N1 influenza and the call for a means to quickly share research information about this critical and emergent public health threat. To address the influenza information sharing need, the Public Library of Science developed PLoS Currents: Influenza, the first collection being archived in RRN. NCBI expects the RRN archive to expand over time to include additional collections in other biomedical fields and other critical topics.
Publishers interested in archiving online, rapid communications in RRN should contact NCBI at RRN@ncbi.nlm.nih.gov. General guidelines for participation are described below; these guidelines are provisional and may change as NCBI gains experience with the new RRN archive.