We have in-floor heat throughout our entire house (and garage!) in the concrete in the basement and under the wood floors or tile on the other floors. My husband is in the HVAC business, so we have a great system that he installed when the house was build in 2004. We do have forced air conditioning and an air handler, so we have the duct work. It costs more to install, but we see a savings in the utility bills.
The radiant heat is great, but it still can feel a bit chilly in the house at times in the dead of winter. Radiant heat doesn't rise like forced air. Your feet are toasty, but your nose may feel a bit cold. It's not quite as nice as forced air heat, but it's not as drying to your skin either. We always have tons of warm water for the showers (due to the large tank that runs the whole system) and our heating bills are a lot less than the neighbors. Our house is concrete, so that helps reduce our bills too. Tons of European homes use radiant heat. If you do it, you definitely want someone with a lot of knowledge to do it.