"The biggest threat to retail, even more significant than softening demand for space, is the entry of big-box retailers such as Wal-Mart, Target and Costco into the grocery business," says Crow's John M. Crossman, senior vice president, Florida retail services division, who authored the report.

"The reason is simple," Crossman says. "The amount of money that people spend on groceries tends to decelerate much more slowly than money spent on luxury items."

He says, "Since competition in the grocery business is beginning to intensify, this stable retail asset is finding itself more and more at risk." But centers in strong demographic locations "should remain fairly well insulated," he told 2,000 attendees at the International Council of Shopping Centers' three-day gathering that ended Aug. 14 at the Hyatt Regency Grand Cypress Resort.