Giant storage radiator? - yes, in a way. Water runs through the fabric of the floor in 'zones' at about 40 degrees (where it enters) and heats the floor surface to about 27 degrees. This heats then convects upwards and heats the house.
One of the better systems IMHO with a lot of info on the website is here
http://osmaufh.wavin.com/master/master.jsp
I don't have this system - I have another one but I'd seriously consider Osma if I was doing it again. Suggest you talk to range of suppliers to get knowledgeable.
Advantages are:
Wall-space not used up by rads
Even-ness of the heating throughout
Control to each room through zones, each with their own thermostat - beter control than TRVs
Disadvantages are:
Almost certainly more expensive to install / requires more controls
Requires lots of insulation below the UFH - otherwise as much heat as comes up will be lost into the sub-base
Can't put thick carpet down - requires wood floors and/or mats (or little heats gets out)
the storage rad effect - slow to heat / slow to cool down. Mine comes on 4am mid-winter and goes off 8pm at night
HTH