The savings from turning household heat down during the day aren't trivial, but they aren't very large either. You can keep your heat ~10-20°F lower during the day when you're not home and save energy, but then additional energy is needed later in the day to get the temperature back up. Typical estimates are that this lowers gas or oil consumption by 10-15%, and only in the colder months. Certainly dwarfed by energy spent commuting, on average.
Your comment on the second+ order effects is much more interesting, but also much more uncertain.
