I think it is important to find a cofounder who you truly respect. besides a few specific skills, the skill set is almost irrelevant since you learn so much on the fly
Co-founders skill sets should be complementary not similar. Essentially, one partner should have a deep understanding of the customer and the other should be able to add value ie. a salesman and an engineer.
that sure sounds like good advice, until you start thinking... how does someone without a sales skillset evaluate a salesman? how does someone without a technical background evaluate an Engineer?