I'm tossing around ideas for building my own house.  I'm decided on using ICFs from basement to 2nd floor and an insulated pad under the basement slab.  Regular board joist floors and a traditional attic with a closed cell foam insulation between attic and 2nd floor ceiling.

I'm probably also going to geothermal that house too.  I really like the idea of in floor radiant heat because my feet get cold easily.  I know geothermal units can be used for the water to water heat.  How would I cool the place though?  I don't really know much about radiant heat, so I have no idea how to cool the house.  Would I just use the geo unit to cool the liquid in the radiant floor to cool the house too?  Seems like my feet would get cold during the summer then.  Please enlighten me. 

You'd probably want to use conventional forced air ac.

Radiant cooling is not impossible but as you said it's better if the radiant cooling is in the walls or ceiling to avoid cold feet. And you have to keep the temps above the dew point so cooling btus are limited in a typical humid summer environment. In that case you'd need a dehumidification system to dry out the air and still might need a supplemental forced air cooling system anyway to achieve the desired temp. Radiant cooling is possible but not very practical for residential in most areas

Got it :)

So do a forced air system and keep radiant in floor as a bonus way to keep my feet warm. Looks like a WF Synergy3D would be perfect for that.

If you are doing a Geo system you will be able to cool as well as heat. To cool you will need to have an air system for the cooling, this can also bring in the outside air with an HRV. Your system will need to be designed to recognize cooling and heating mode on the buffer tank of the system. You will keep water at 110 for heating and deliver it through the floor in the winter, also can use the air handler, in the summer your buffer tank will be kept at 40-50 deg for cooling using only the air handler. Unless you live in a dry climate and can keep the cooling in the floor 5 degrees above the dew point you will risk mold with in floor cooling, plus as I am told cooling with slab can be uncomfortable.
Dan