For us, we were at idea stage when we applied to YC. The application process has motivated us to start something whether or not we get into one of the 'combinators this summer (some decisions are still pending). That's an awesome kick in the pants. Applying to YC was a great opportunity to find out which of my peers were interested in startups and to get started on something. We're both still in school, so we have good circumstances to get going regardless of the decision.