The National Science Foundation (NSF) and the Directorate for Geosciences has issued a Dear Colleague letter on Data Citation in the Geosciences that is very timely and relevant.
Additionally, the National Center for Atmospheric Research (NCAR) is working on a draft policy for data citations, Data Citations in NCAR/UCAR (2012). This is a very good overview of the importance of accurately and consistently citing data sets, including DOIs, for discovery and tracking data use and history, just as we track refereed papers.