The Japanese were playing 1980 Texas-style land-flip games writ large (i.e. massive speculation), plus they have a rule that lets banks count the value of their real-estate into their whole stock market valuation equation.If you see homeowners buying their homes one day and selling it the next day for 40% profit, then yes, you are witnessing a bubble on the rise.
It's extremely rare to see that sort of thing in residential real-estate (i.e. primary FNMA territory).
Unless you are seeing "Demand" getting juiced up by speculators, then there probably isn't a fundamental structural problem with American real-estate.
American corporate real-estate is priced lower than that in Moscow, London, and Tokyo, so if there is a bubble in commercial real-estate, we'll probably see it pop over in those locations long before it happens here (and I doubt that anyone seriously thinks that Japanese real-estate could still see massive new devaluations).
Home buyers in America are spending less than 30% (on average) of their incomes on their home mortgages, and more than 60% of American homes are owned debt-free (e.g. hi mom).
The fact of the matter is that people are willing to spend up to 50% of their income on their homes. Banks will easily loan up to 35% of your income, too.
But that's a long way from a collapse in home prices or a massive wave of defaults.