To judge from the buzz coming out of the International Builders Show in Las Vegas, the McMansion may be finally going the way of the McRib.

Of course, we've all heard that before. For years, journalists have been writing stories about how rising energy costs are forcing a shift away from suburban trophy homes in exchange for something more efficient and intimate. Meanwhile, builders continued carpeting suburbia with tract homes and consumers couldn't get enough. But this time, it seems we may have really reached a tipping point.

"We never had any data to back up (the trend.) This is the first time," says Gopal Ahluwalia, vice president of research for the National Association of Home Builders.

The data he s talking about: Survey results that show that both consumers tastes and builders habits are changing. The catalyst, though, seems to be not so much the desire for "green" living as the double whammy of a slumping economy and shifting demographics. The latter is perhaps most vexing to builders: after years of catering to baby boomers, who generally believed bigger is better, builders now have to adjust to the whims of Generations X and Y.

Among Ahluwalia's findings, presented Wednesday morning:

- The average size of homes that went under construction dropped rather precipitously in the most recent survey, from 2,629 square feet in the 4th quarter of 2007 to 2,438 square feet in the first quarter of 2008. It was the first significant decrease in more than a decade. Homes completed in the first quarter of 2008 were as big as ever, which seems to indicate that once builders changed their ways, they changed fast.

- The average American lives in a home that is 1,835 square feet, but would prefer to live in a home that is 2,354 square feet. In other words, the buyer s ideal home is still smaller than what builders are building.

- 58 percent of consumers surveyed said they would prefer a smaller home with top-flight amenities than a bigger home with fewer amenities.

- In a survey of builders conducted earlier this month, 88 percent reported plans to build smaller models going forward. Similarly, 89 percent reported plans to build cheaper homes.

Bolstering Ahluwalia's findings, Better Homes and Gardens editor-in-chief Gayle Butler presented her magazine's in-house research showing that readers want "right-sized" homes that are functional, not super-sized ones with features that feel superfluous. "We hear from Moms that as homes got bigger, they felt their family activities scatter," Butler says. In: built-in cabinetry and cleverly-hidden storage spaces. Out: kitchen desks for Mom and formal dining rooms.

Of course, as the Big Three in Detroit can testify, Americans don t always put their money where their mouths are where greener and smaller are concerned. For example, in the same homebuilders survey in which Americans claimed to want smaller homes, 52 percent said they want a home with four bedrooms or more. "We're still adjusting expectations," Butler says.