I live in Italy, work for a real estate developer and thought this might be of interest.  One of the large Italian curtainwall contractors is getting into the radiant heating business and showed us their new product. 

It is 15mm (±5/8") drywall laminated to a sheet of 27mm (±1-1/8) styrofoam insulation.  The back of the drywall has small tubes (they look like 3/16" ID) embedded about 2" OC.  The product has been designed to be used in both ceiling and wall modes.  The finish side has lines marked on it to show the tube locations.  They also have special picture hangers with three short nails.

You can see thier website here <http://www.fccplanterm.com/eng/index.htm>  The tanslation, like most, leaves a bit to be desired, but you will get the idea.

Ciao,

Bruce