Where can I get more information about US reference frames and epochs?

You can find more information about the new NAD83(NA2011) National Spatial Reference System on the NGS website.  The new SmartNet coordinates (effective October 1, 2012) tie to the NSRS within the requisite 2 cm x 4 cm set forth in the NGS RTN Guidelines.

Explaining NAD83(NA2011) - http://www.ngs.noaa.gov/web/surveys/NA2011/