http://www.hbosplc.com/economy/includes/08_04_08HousePriceIndexMar2008.pdf
The underlying strength for the US is the world economies, which is still growing, if you look at exports, truck tonnage, and the Dow Transports are all holding up relatively well compared to the 2000-2003 downturn.
However, the prospects for the global economy are actually worsening, because they are all approaching their own prospective tops in the Real Estate cycle. Leading indicators for Europe, Asia and even Canada are turning down; as well, the markets continue to tighten offsetting any monetary easing by the central banks.