I interview a lot of programmers, and I can tell you with about 95% precision whether they will work out and be great based on the single question 'tell me about the programming projects you work on for fun'. If they have some project they work on for fun, even one, that isn't for a class at school or for their job, then they are very very likely to be a great hire. If they don't they are very very unlikely to be a good hire. Side projects don't magically make you smart and capable and good at problem solving and getting things done, but it sure seems to be fundamentally related.
And from personal experience, I've worked for 2 startups, one where people worked all weekend and one where they didn't, and interestingly they were doing almost the exact same thing. One had an $80MM exit, the other just slowly went away. Small sample size, for sure.