As long as you aren't doing any WOT driving when cold you will not do any harm. Letting an engine fully warm up before driving is nothing more than a waste of gas, time, and possibly extra wear. When it's really cold it doesn't hurt to run it for a minute to ensure oil is everywhere, but after that you should just drive it. The engine will warm up much quicker that way, and the quicker it gets to operating temp the less wear will take place.
