!!!Some spoilers from the books may follow.!!!
Winter in Westeros is a major recession; in particular, it is a real business cycle (RBC) recession as it decimates agricultural productivity when agriculture is the largest and most important industry. In some (or most?) parts of the country, agricultural output falls to something close to zero.
I always think of two major mistakes the Westerosi are making with respect to their business cycle. First, they are not saving enough. Second, they are not sufficiently focused on technology.
This is really puzzling behavior from heads of houses who seem to care a lot about the future of their brand. It seems like these people should be making huge efforts to store food. The only reason to buy weapons is to protect your storehouses. The only reason to build castles is to protect your storehouses. The only reason to mine gold is to buy food, buy food storage technology, or buy castles and weapons to protect your storehouses. And so on.
The Starks, whom a lot of readers are inclined to like, really look bad in this context. They have the most to lose from Winter--they are the first to enter and the last to exit winter, and their winter is likely the hardest. So why is Ned accepting a job in King's Landing when he should be scrambling to prepare his jurisdiction for winter? Even worse, why does Robb leave home to pursue a revenge war whose ostensible purpose is to gain independence from a monarch who won't even matter when winter comes? This is seriously reckless and irresponsible behavior.
As summer drags on and on, the Starks' time should be increasingly occupied by building huge greenhouses and building huge walls around them (Eric Crampton has noted the greenhouse issue). There's really no excuse to focus on anything else, unless it's figuring out a diplomatic solution to the Wildling issue or, depending on your priors, fortifying the Wall against the Others. When Robert Baratheon shows up to hire Ned as Hand, Ned should be laughing him out of the North. "Me, come to King's Landing when my people will be the first to suffer in winter?! No way." And at the very least, he goes only on the condition that he's going to play Joseph of Egypt (or Andrés Velasco) and make the realm's famine preparation agenda his top priority. If he does that, he gives Catelyn and Robb strict instructions to carry on his work preparing the North. No silly excursions south when our people aren't ready.
So the Starks are idiots. Most of the other houses are too. Frankly, Tywin Lannister seems far too smart to waste time and resources on the war when he should be sending cartloads of gold to Highgarden in exchange for food (Matt Yglesias has touched on this before). And even if you do go to war, you don't go around gratuitously burning other peoples' fields. When winter comes, you want other people to have food too (so you can take it, or at least so they don't come to your door).
Maybe you end up saving too much. But, as I mentioned to Jim, that just means you'll have a chance to buy other house's assets at fire sale prices during winter. You may come out of winter with not only a full belly but also a new fleet of Iron Islanders' ships and a portfolio of Lannister gold mines.
We do see a few people taking things seriously. I don't know if we hear it explicitly, but it seems very likely that the Manderlys are on top of this. They seem to have a pretty long game generally. Wyman stays home and lets his sons fight the war, and we later learn that while home he's been focusing on a lot of long-game preparations. We also learn from the new Winds of Winter Sansa chapter that Littlefinger is getting things ready too (of course, as Master of Coin he really should have been focused on this at the realm level instead of selling royal debt the whole time).
One other thing. My friend Jack has this to say:
The savings problem is precisely why the Lannister-Tyrell schism of A Feast for Crows and A Dance with Dragons is so important.The Tyrells came into the War of Five Kings very late so they still have much of their military, agricultural, and economic might, and Cersei just alienated them by having Margaery thrown in jail for adultery and treason. This is happening at the same time that Winter Is Coming and Aegon is taking castles in the Stormlands.
So Martin is likely to do something with this in coming books. I hope he takes it seriously. So far, I have a hard time making sense of the behavior of some of these houses.
UPDATE: Matthew Klein notes, "the food isn't grown in the North. If anything he should have focused on evacuating his subjects down to Dorne." Good point. Getting out of the North seems like a decent priority.