The main costs of say a YC startup are living costs - in a downturn, these should drop. Raising second round funding will be more difficult, sure. But in times of trouble, people cut back on bars and stay in, and will spend even more leisure time online. I see the ecommerce space surviving this very nicely; ads will take a big hit; and god be praised there will be less unjustifiable multi-millino M and A's of small start-ups that have not even reached revenue stage - start up entrepreneurs will be forced to actually build a business!