Sharing data that you create through a project funded by a federal agency, foundation, or other research sponsor is an important component of your data management plan. As stated within the NSF Data Sharing Policy:
"Investigators are expected to share with other researchers, at no more than incremental cost and within a reasonable time, the primary data, samples, physical collections and other supporting materials created or gathered in the course of work under NSF grants. Grantees are expected to encourage and facilitate such sharing." (http://www.nsf.gov/bfa/dias/policy/dmp.jsp)
See also AU Campus Resources for data sharing and management planning.