I'm looking at using this as a ceiling in my pole building to help hold some heat in. Anyone have any experience with it? Seems like it might be a good way to reflect some light in the building and hold heat in without having to get the full-finishing route.

links
http://www.dow.com/styrofoam/na/res-us/products/thermax_sheathing.htm
http://www.silvercote.com/PDF/ThermaxAGThermLit.pdf

I've never used that stuff that, but I have used a reflective cardboard type insulation - like this stuff only it was in sheets:

http://www.insulation4less.com/highr_FBF.asp

Works great, but the room I did was only 20x20, so I would think the stuff you want to use would work fine

Thermax is Polyisocyanurate. It's roughly R-6 to the inch. Works great for the first couple of years, but will degrade with time. It does not like moisture, and it will soak it right up--further degrading its insulating properties. Keep it dry, and it's probably one of your better options for what you plan to do.