I've been contemplating this in one of my garages. I would go with the electric mat style of infloor heat.
Possible install method:
clean the existing concrete
put down a concrete bonding primer so the skim coat bonds to the old concrete.
Laydown some reflective foil (if I can, to help insulate)
lay out the infloor matting
Put down a skim coat of self levelling concrete.

Has anyone tried this? Did it work out? Did you insulate the floor?
My concrete slab is about 1 ft thick, I just don't want to go through this to find out it barely warms up.

I was hoping that because it's closer to the surface that it would be like a warm mat on the feet within 30min of turning it on. I'm not after warming the air. Other data suggests that heat loss to the concrete would prevent the heat from really making a difference on the floor surface.