It would screw up high-noon for a lot of people. However, getting the US down to two time zones would be much less problematic, and achieve most of the benefits you'd see from one time zone...
But seriously, look up how time zones work in China. The whole country is on Beijing time so the western areas essentially maintain two clocks because the "official" clock is so far off the day/night cycle.
http://www.theatlantic.com/business/archive/2013/11/daylight...