The tricky strategy of all-you-can-eat.

All-you-can-eat deals are also sometimes bundled with side dishes or as part of a combo meal. In some cases, the wait staff is trained to enforce the "clean-plate rule": Just like at Mom's, you can't have the second- or third-serving until you've eaten what's already in front of you; otherwise the endless dinner could become the endless doggie bag. There are also some subtle visual cues—such as using smaller plates and waiting longer to clear empty dishes from the table—that can keep diners from eating a restaurant out of business

While some types of restaurants make all-you-can-eat their raison d'être, most of these recent promos are limited-time offerings—LTOs in industry parlance. According to an industry analysis by Technomic, LTOs—which include all-you-can-eat offers as well as new or seasonal menu items—are at a five-year high. Restaurants like LTOs because the format lets them test a new pricing format or menu item without a long commitment. LTOs also work because they rely on scarcity theory, according to Brian Wansink, author of Mindless Eating: Why We Eat More Than We Think. Creating an artificial sense of urgency is a successful gambit used by businesses ranging from car dealers to electronics retailers.

There are other psychological factors at work, too. Even if diners don't avail themselves of the all-you-can-eat option, they still perceive the brand as one that offers a good value, says Wansink. It's a way for restaurants to brand themselves as value-conscious without lowering their prices. Dropping prices is a risky move because unless you're a fast-food giant, there's always going to be someone that sells a meal for less. What's more, a lowball strategy might get people in the door, but it also sets up an expectation in the consumer mind that's difficult to rewrite. The hospitality industry offers one recent cautionary tale: Hotel companies that slashed their rates after Sept. 11 to lure back travelers encountered stiff resistance when they tried to raise them again. Even in relatively flush New York City, it took four years for hotels to get back to pre-9/11 levels.

The other big risk with all-you-can-eat pricing is a sudden spike in commodity prices. Darden Restaurants' Red Lobster brand is the poster child for this squeeze; in 2003, an all-you-can-eat crab promotion turned into a loss for the company after the wholesale price of crab nearly doubled unexpectedly. Now, though, with wholesale food prices down by nearly 2 percent in October, restaurant operators' collective concern is shifting from food prices to the impact of the slumping economy on their bottom lines.

Customers have their own bottom lines in mind, too. Analysts say a growing number of diners are using all-you-can-eat offerings as the opportunity to have two—or even three—meals in one by stuffing themselves and skipping the next meal, then earmarking any leftovers for the following day's lunch. Whether or not they follow through on their planned restraint is anyone's guess, but this binge-today-fast-tomorrow line of thinking can be profitable for the restaurants that feed it.

Indeed, most restaurants no longer refer to their gluttony-fests as all-you-can-eat. Instead, they prefer adjectives of abundance: bottomless, endless, unlimited. It's a small switch but psychologically significant. In an atmosphere where everything from job security to credit is limited, there's a strong gut-level appeal for the promise of something—even if it is only flapjacks or fettucine—that stretches on forever.