Some homeowners struggle to keep up with adjustable rates
Of the 7.7 million households who took out ARMs over the past two years to buy or refinance, up to 1 million could lose their homes through foreclosure over the next five years because they won't be able to afford their mortgage payments, and their homes will be worth less than they owe, according to Cagan's research.

The losses to the banking industry, he estimates, will exceed $100 billion. That's less than the damage from the savings-and-loan crisis in the 1990s, which cost the country $150 billion. "It will sting the economy, but it won't break it," he says.