I bet stable founders have more stable relationships with their SO's.
Dave Ramsey writes about how his company uses dinners with spouses as a part of their interview process. They won't hire anyone "married to crazy". They also fire anyone who cheats on their spouse. I found his book quite misogynistic and offensive (not to mention having the worst title ever), but I wonder if he's onto something.
The idea of YC (or any company) using personal relationships as part of their filtering process makes me extremely uncomfortable, but it's interesting to think about.