When you first upload a dataset (or if you later chose to edit it), in the metadata you can set permissions. From the documentation:
You can also set permsissions for specific groups of users, say, if you want to share certain levels of access only with particular colleagues.
Note: Once a map has been saved in GeoCommons, you can click Edit in the upper right to make more changes and re-save it.
From the search results page, you have an option of downloading a dataset (if the creator has set Access permissions on it).
Formats are CSV, KML, and zipped Shapefiles.