Don't forget non-compete agreements - valid in NY, invalid in CA. So not only can you NOT leave your day job for a startup, you typically have to wait 2 (or more) years before being able to freely work on any projects. (If your start up is in a completely different area than your day-job, you may be able to get away with it sooner. But don't think that corporations are lax about enforcing the non-compete you signed.)