From my experience pouring over stats like this a few thoughts.
Sales are astonishing stable. In fact, when sales seemed to be lowest in SD County (2nd half 2007) they were highest in 4S.
Sales are slowing in 4S and should continue to do so because more will involve bank approvals for short sales which slows done the process.
Lower market pricing even by $25K can push a seller into short sale terrritory. It would be a rare 4S owner that bought new in 2005 or 2006 that isnt underwater, even those who made reasonable down payments. If forced to sell, most will result in short sales.
2009 and 2010 will be the years of the short sale in communities like 4S so prepare for long waits. IMO, this will restrict supply and slow down the sales process to allow the lower end homes to retain value relatively well. Dont expect to see $450K for a 2300 sq ft home anytime soon.
Loan modifications can help in an area like this where people have real jobs. Whether they will be at a level that actually makes a difference is yet to be seen, but they could definitely make a difference.