With all the new electronic dimmers there seems to be a need for neutral conductors at switch locations. This new code section in the 2011 NEC requires that if you cannot access a switch box after the installation then a neutral conductors is required to be installed in the box. If you can access the box after the installation then the neutral will not be required until it is needed.
This is a 2011 code change and will not affect installation being done now but when it is adopted this will be something all the inspectors will be looking for.
Until next week
Be safe, always check to see if it is hot.