I'm not pushing for anyone buy, but at some point in time risk has to be taken. Sure, a person could lose their job or have some other catastrophic event come along. That's going to happen no matter if you're an owner or a renter. Life is a risk, isn't it? You can't plan around every single contingency.
A $400k home with 10% down means that at minimum the $40k down is at risk, with a possible $40k also at risk if prices decline another 10%. That additional 10% loss should be considered, but it's as theoretical as were all of the 50%+ appreciation gains.
All of this assumes you're not able rent, not able to sell, and not able to make the payments no matter the circumstance. At that point, your problems are not simply housing but much, much more. With a real employment rate of 85% (15% real unemployment) there is a risk of a person losing their job - but it depends on the industry and the ability to be re-employed quickly.
At some point a floor in prices will come - not a bottom - a floor. The same for employment. Most "big bears" believe 2011-2012 will be the floor for housing. That said, a 5 year outlook is reasonable if your risk tolerance is high.
My .02 - SGIP