The non-commercial restriction the least clear of all of the licensing terms. The commons deed describes the non-commerical restriction as " You may not use the material for commercial purposes." with an additional description of “primarily intended for or directed toward commercial advantage or monetary compensation.”(emphasis added).

Determining if a use is "directed toward commercial advantage or monetary compensation" depends on the specifics of the situation and the intentions of the user. Importantly, the type of user is not a major factor. A nonprofit or charitable organization could violate the NC restriction, and a for-profit entity, even one receiving monetary compensation, does not necessarily violated the the NC restriction. 

Creative Commons has an FAQ Entry and a brief wiki style guide that goes into much greater detail on how to interpret the NC license.