Parked my 2011 Impreza WRX outside for 24 hours (low temp 7 deg F) Sunroof had apparently cracked throughout due to cold because pressure change of closing the driver's door caused the thing to shatter and fall in on liner. Anyone ever had this happen or hear of it happening?

Wow, not cool!  I assume you have reported this to your local Subaru dealer?  I believe it would be a touchy one to cover but one that would likely get covered by most dealers after a call to the regional representative.  At a minimum it would seem like one to cover as a good faith thing even if its not 100% certain its the fault of the car maker.  

I have heard of it happening to the sunroof panel in the wierd dual sunroof outbacks, but not the normal sliding sunroof panels. That glass is usually unbelievably strong.