Jamie Zawinsky, netscape founder, referring to this Michael Arrington article which urges startup founders to stop complaining and get back to working long hours and sleeping under their desks:
Follow the fucking money. When a VC tells you what's good for you, check your wallet, then count your fingers.
So if your goal is to enrich the Arringtons of the world while maybe, if you win the lottery, scooping some of the groundscore that they overlooked, then by all means, bust your ass while the bankers and speculators cheer you on.
Instead of that, I recommend that you do what you love because you love doing it. If that means long hours, fantastic. If that means leaving the office by 6pm every day for your underwater basket-weaving class, also fantastic.
A healthy attitude. Startups are about working smarter than the competition, not about working longer hours. One good idea emerging out of a good night of sleep can save you a week of work. Don't skimp on sleep.