Radiant floor heat is considered by many to be the most comfortable method of delivering heat. Even zero energy homes need a source of backup heating. Therefore, radiant is often the choice in high end custom homes, when cost is trumped by comfort and "sizzle".
After building and living in a near zero energy home now for three years, we have learned that radiant heat is quite comfortable when it is on. The trouble is, the solar and superinsulation aspects of the house prevent it from coming on very often. In fact, it hasn't been worth the extra cost of the system (about $10k more than a forced air system), and we wouldn't do it again.
Additional challenges with radiant floor heat:
1. A completely separate ducted system is required for summer air conditioning. A swamp cooler in Denver is by far the best choice (it typically won't use ductwork).
2. In order to filter, humidify, and ventilate, a separate ducted system must be installed. (Now add $5k to the above $10k).
3. The heating system is at risk of freezing in extreme conditions with a power failure.
More lessons learned in a superinsulated home:
The third floor attic bonus room has no heating source, and this turned out to be a mistake. It was designed without heat because in my experience, third floor attic rooms were always the warmest place in the house. It turns out this is only true if the heating system is running a lot. In our house, since the boiler is rarely on, the third floor doesn't get enough heat from naturally rising warm air. The third floor, therefore, stays about 4 degrees cooler than the main floor.
Close attention was paid to the basement insulation details. As a result, the heat loss is so low that the basement zone comes on only about 4 times per heating season. Again, that zone wasn't worth the cost when a couple $30 baseboard heaters could do the job.