I wouldn't work for a startup, unless the pay was higher than than market (since there is more risk involved). I would also treat it as a job (IE: no insane hours).

All too often, people toil away their life for someone else's idea and then get kicked to the curb (it's happened to me a couple times too). If I'm going to be wasting my free time working, it's going to be for the possibility of a big payout..which will only happen if I own the company.