Well, I just finished entering the first tank in my wife's new Prius. All in all, not too bad considering it is the first tank and we both drove the vehicle. However, we're getting ready for much worse mileage perhaps edging on the very low 30's (if we're lucky... but this is far better than the Acura EL which would get 18mpg in the colder months).
This will definitely have an impact on the GH DB average for the model... so my apologies to all Prius owners. On the other hand, it will be worse for the HCH-II crowd because I will likely enter a few more tanks over the winter for my HCH-II (my daily commuter).
Fortunately, our summers can be pretty long too, enough to hopefully have a higher overall average for both. But I admit, in weather like this we often talk about moving south for the winter: Just like the birds do.
Cheers;
MSantos