NPR asked this question. In my opinion, it will be when we have jobs and the prospect that we will keep them in the future. Then we will feel good enough about things to buy again. Of course, I also am convinced that the economy will not come back like it was, because much of it was build on deception and wrong thinking. People live beyond their means when they're optimistic. They are ready to believe that something that sounds too good to be true is actually true because they see others making it big.
Get ready for the long haul poor economic conditions and prospects.