Today's SF Chronicle: 9% decline for 2008

Forecasting a 9 percent decline in average home prices on the statewide level in 2008. And he said an additional 15 to 20 percent drop in 2009 would not be out of the question.

"We disproportionately enjoyed much higher home price appreciation over the last several years with the uses of subprime and Alt-A loans," Adibi said. "This is going to come to haunt us."

In the last steep housing downturn, Adibi said, it took 54 months for San Francisco home prices to fall from peak to trough; in San Jose it was 60 months, and in Oakland it was 51 months. To get back to the previous peak price levels took another 3 years, roughly.

"I don't see anything that would suggest the current downtrend is going to level off soon," said Michael Carney, executive director of the Real Estate Research Council of Northern California. "In fact, I think we might be seeing a gathering of momentum in the downward direction. I think we're more toward the beginning of a process than toward the end of it."

The median asking price for a single-family house in San Mateo County, for instance, has fallen from $948,000 in November 2005 to $767,000 this November.

The average number of days on market, meanwhile, has jumped from 59 to 100 in the same period. Most distressing to Calhoun, who studies home prices and sales each month gleaned from MLS records, is the number of sales - only 517 in November in Santa Clara County - the lowest number for any month since 1998.