I haven't changed my retirement portfolio at all, even though my Internal Rate of Return for 2008 was around negative-38% overall. Here are my reasons:
I felt good about my asset allocation before all of this happened, and I have no reason to believe that any other allocation is going to perform any better in the future.
I have a portfolio that has tracked well with the overall market.
I really don't want to retire for another thirty years, if then.
If the stock market goes back up in thirty years, then I'm buying on the cheap, and will be doing GREAT for having stayed the course now.
If the S&P does not go up for thirty straight years, my retirement portfolio will be among the least of my worries. In such a circumstance, we'll be facing worldwide chaos. I'll be poor, but so will you and everybody else.