JPA - I think you and I had talked about this before in your theater thread as you were building your house....what kind of cycle times are you getting with your system? Sometimes the efficiency of the spray foam and windows makes it so that your system runs long enough to get to the correct temperature, but not long enough to dehumidify. There could be some adjustments made to the system itself or in the more sophisticated areas of thermostat programming that will allow your system to run longer to dehumidify.
One of the challenges in our house that has 3 separate systems is that we have an open floor plan that acts like a chimney. We literally have to keep all the doors closed in the upstairs hallway to allow the heat to permeate on the main level when the MAIN level system is running. If we didn't shut the doors, all the heat simply fills the bedrooms and the first floor works a lot harder in the winter because it is essentially heating both the first and second floors. The reverse is true in the summer where we keep the doors closed yet again to keep the cool in the bedrooms. The only bad part about this is the builder didn't put returns in every room, so having a room constantly pressurized with only supply doesn't really move or mix the air well....at all.
I think the Nest is cool if you are in a single-system home where the Nest's sensing capabilities were able to fully work by having the thermostat in a prime location in the house that sees any of the traffic. But like Fred says, I think you can do just as good of a job by properly programming the right kind of programmable thermostat that has 4 set points throughout the day. Since you have a multi-zone system, I would probably just stick with the programmable thermostats specifically designed to run that system.
As for temps....we usually set the thermostat at 76 or 78 over the summer and 68 or 70 over the winter and we never heat/cool more than 5 degrees from our daily max / min temperature. Anything more than 5 degrees and you are wasting energy. Ideally you want the humidity right around 30%-55%, but most aim for 45% as "comfortable". Since you are in the deep South, you probably ONLY need dehumidification year round I am guessing. That is what we have here in Charlotte. Up in Pennsylvania we had a humidifier and it was definitely needed, that's for sure.