My father would swear by the fact that a regular freeway trip for his car would help its fuel economy even when it's just running around town. He used to call it letting the car "stretch its legs" and it did seem to make a difference. His fuel economy improved, not just for the tank that did the freeway trip, but for a few afterwards as well. Might just have been that car, haven't put it to the test myself. I don't keep records as accurate as my father, either - he has a little book in the glovebox where he records the date, the km travelled and how much fuel he's put into the tank. Of course, he always fills the tank completely every time he goes, doesn't work if the budget is tight and you can only put say $10 in to get through the next couple of days.

BW
I agree with this. Ours is a Ford Territory and I think it'd cry if it only got a chance to do the little driving I do in a week I give it a go every few weeks, might go the long way to visit my mum where there are 100km/h roads. I think it always runs better after that. We've done a couple of long highway drives in it and it just cruises, loves it. This weekend we're going to Mildura and we won't be towing, so we'll see exactly how many ks it gives us on the highway.

ETA - Tinks, my friend just took his Mazda 323 to Adelaide from the northern suburbs of Melb - and he got there on one tank of fuel. Nice efficient car you've got there!