This isnt your usual recession and movement of people isnt created equal.
First off, in a usual system companies fail, and that causes layoffs and that causes demand to fall and that causes more companies to fail etc. The economic system isnt hit until demand falls. This time around demand fell, but the companies were all ok (on the outside atleast) and that is why everyone wasnt forcasting a recession. But now companies are failing (ALA bear stearns) and jobs are disapearing (read the jobless claims out today, highest since 2004) and it is all kinda backwards. People still had jobs and incomes and savings and hope last year. As each of those are taken from them in a downturn they will leave to greener pastures elsewhere.
Second off since they related it to the housing market, I will too. Net immigration into SD is positive entirly due to foreign immigration or due to birthrate. Basically wealthier, older and traditionally whiter people are moving out and younger, poorer and traditionally non-white people are moving in. Where you use to have households of 2-3 people (dad, mom, and maybe a kid) you now have a household of 5 (Dad, mom and 3 kids). So population may be going up, but demand for housing isnt necessary. For the next 15-20 years you could have 40% more population with the same demand for housing. This will hit the middle income areas the worst, (Chula, Poway, MM, Nat.City) as their housing stock is smaller, older and traditional middle income buyers are the ones not hanging around.
Maybe I am wrong, but until prices hit a point that the newer, less well off population can afford, demand for these areas will be worse. The good news is that in 20 years there will be alot more demand for housing again. All of this ignores the macroeconomic system ofcourse (if jobs fall, will people still immigrate or have as many kids?) but we are talking population in this thread, not interest rates.