others have summed it up pretty well, with the "no false positives" perspective. But, I will play devil's advocate and say: Make sure you aren't just looking for "someone like me", and finding no one measures up. I've noticed this in some younger founders...there's a pair of folks who are nearly identical in skills, history, and goals, and this is not necessarily a good mix for success in a startup. They get along great, but they aren't a good team.

You both need the same drive to build something great. But you need to have different skills, different areas you enjoy working on. If you don't, you'll fight over the mythical bike shed and the hard solitary work won't get done. And there's a lot of hard solitary work in a startup.