I can hear the chorus of HNer's working at startups saying "yeah, but just wait until we go IPO or get bought or go viral then you'll see why we worked so hard so late so often for so long..."
I think this work / life separation is really important (to me at least). I don't personally think that what you do at work represents who you really are, and having activities outside of work defines you way more than that thing you do from 9 to 5 to earn a salary. In the end, a job is only there to provide you enough money to pay for your lifestyle.
If your personnal goal is to be crazy rich, then go and work your ass off like crazy for years. But when your job pays enough that you can keep your current lifestyle and you like what you're doing like this, I don't see anything that would make me leave BigCo for a startup filled with dreams of being rich.