Alan Greenspan's semi-annual economical outlook speach to the Congress mentioned the frothy housing market again.

thebubbletalk.com quotes Greenspan: "three major threats to the sunny economic outlook. First, the possibility that wage pressures, which have been dormant, will intensify. Then, the threat posed by surging energy costs and finally, the dangers posed to the housing market if long-term interest rates rise significantly."

Greenspan's comments specifically on housing market boom:

"Whether home prices on average for the nation as a whole are overvalued relative to underlying determinants is difficult to ascertain, but there do appear to be, at a minimum, signs of froth in some local markets where home prices seem to have risen to unsustainable levels. Among other indicators, the significant rise in purchases of homes for investment since 2001 seems to have charged some regional markets with speculative fervor. The apparent froth in housing markets appears to have interacted with evolving practices in mortgage markets. The increase in the prevalence of interest-only loans and the introduction of more-exotic forms of adjustable-rate mortgages are developments of particular concern. To be sure, these financing vehicles have their appropriate uses. But some households may be employing these instruments to purchase homes that would otherwise be unaffordable, and consequently their use could be adding to pressures in the housing market. Moreover, these contracts may leave some mortgagors vulnerable to adverse events. It is important that lenders fully appreciate the risk that some households may have trouble meeting monthly payments as interest rates and the macroeconomic climate change. The U.S. economy has weathered such episodes before without experiencing significant declines in the national average level of home prices. Nevertheless, we certainly cannot rule out declines in home prices, especially in some local markets. If declines were to occur, they likely would be accompanied by some economic stress, though the macroeconomic implications need not be substantial."