Take all the houses now on the market, add in all the houses the banks have on their 'to do' list, then add in all the houses that will most likely end up in foreclosure as the months go by. Divide by the going monthly sales and find there is a 9 year supply of homes waiting to be drive down housing prices.
Suppose sales really pick up. Up by 200% or 300%. Then there would only be a 3 year or 4 year supply of houses. 3 years to clear all of the houses, not including yours, which need to be sold.