Joe,

In the winter months we used to get diesel supreme from the Standard Oil distributor and had good luck during the winter months. In the last few years (since BP, Amoco,TA and Petro have been rolled up) here we've had our decent service with Shell diesel during the winter months and even without additional additives it seemed to get better economy and no jelling.
I've seen kerosene added to already blended fuel and even have customers that will add gasoline(small amounts maybe 5 gallons a side) to their fuel when the temps drop to -20F and stay there for a while. Trukster - isn't #1 and kero the same (without road use tax, of course) in the 70's many owners of 238/318's ran either without many problems, as fueling options were mostly limited to the main highways.
Personally I like Power Service products and use their cetane boost / conditioner year around and anti gel when I'm north of the Mason-Dixon in the winter months. Fuel quality sure isn't what it used to be! I park my camper in a heated garage during the winter months, so I probably don't really need the anti-gel as the return line temp and coach heaters should keep the fuel warm enough not to jell up when travelling - as related in Jon's experience.