Have to run the car for 1/2 hour otherwise you risk running metal on metal in the engine - oil is thick and takes a while to warm up. Should have hear what my car sounded like when I started it this morning.
I'll leave you with this image:
This is what one looks like in winter in Montreal.....if you brave the outdoors that is (I love my car).
Much thanks to the Gazoo (aka the Montreal Gazette) from whence I stole the photos :)