While NAC is an interesting concept, it is at heart still a mostly proprietary system. Geoaddressing is not a new concept - the military (NATO forces in particular) have used the Military Grid Reference System for such purposes for decades. MGRS and its civilian counterpart, the US National Grid provide a unique advantage over NAC as they permit both point and area referencing based on context sensitive use and permit variable precision and accurary. By way of example a water valve located at a street intersection would be coded as a 10-digit number under normal use circumstances, an apartment would require 8 digits, and something large - say a football stadium - one could make due with either a 4 or 8 digit number. Before I get flamed on this - yes we understand that UTM zone junctions are not nice neat boxes. However, for map users this is not a problem - how a coordinate/geoaddress is read and used is consistently applied. For more information about the US National Grid/MGRS (the difference between the 2 is the datum NAD 83 for USNG, WGS 84 for MGRS - not of significance until sub-meter measurement is required), please visit:
http://www.fgdc.gov/usng <-- note that this is a US standard - the ONLY coordinate system for which such a standard exists.