The blazing-hot topic at suburban cocktail parties this spring is whether there's a bubble in the residential housing market. No wonder. In 2004, existing home prices rose faster than in any year since the 1970s. Some markets are going bonkers. Alexandria, Va., is up 31% in 12 months; San Bruno, Cal., 25%; and parts of Manhattan, more than 50%. A front-page New York Times story featured a Florida couple who had bought and sold four properties -- two condos and two houses -- in the space of six months, clearing $500,000. And none of the homes had yet been built!...