Inventories, both actually available and hidden, are huge in many parts of the country. Foreclosures will likely exceed sales for some while, which will tend to increase inventories even more.
Prices have a ways to go down in many markets, and have been held up by contrivance. First time homebuyers' credit, now gone. Stimulus spending, under threat. Low interest rates, under pressure. Extended unemployment benefits, soon to disappear. The only reason unemployment numbers look as good as they do is because lots of people have recused themselves from the labor market, electing to become stay at home moms or dads. They'd be actively seeking work, if they thought they had a prayer of finding it.
Historically, America has sustained median house prices at 4X median income in a regional sort of way, and we're still well above that.
The only reason prices are as high as they are is because the FRB gave cash for crap MBS, which were backed by crap mortgages. The FRB can get away with taking losses. Banks are under little cashflow pressures to foreclose & sell properties where they never securitized the note. The bailout also took off the pressure. As servicers, stretching out foreclosure & sale allows them to divert monies due investors to themselves as fees, and to hold up prices thru reduced inventory.
Whatever measures necessary to hold prices flat or allow for a slow decline will likely be taken by the govt. Their objective is to get strapped underwater homeowners to hold on, achieve equity via payments over longer timeframes than in the past. If prices decline too far too fast, homeowners will opt for strategic default in droves, blowing the bottom out of the market in a death spiral sort of way, as in the early years of the Depression...