Talk about timing - pick up the Feb issue of Car and Driver magazine for an editorial on how driving habits & style affect mileage. The context of the editorial is about hybrid vs. non-hybrid versions of the same model, but that doesn't matter.

PS - warmer weather makes for better mileage, as most of us must have noticed. I don't know whether it is the higher temperature of the air or the lower density the vehicle has to push through, but this rule has been constant on every car I have ever driven.