Jeff Immelt, CEO of GEO (http://www.businessweek.com/magazine/content/02_04/b3767079....) boasted that he worked 100 hour weeks for two decades.
I've heard plenty of stories of people working crazy hours (the Mint.com guy built his prototype doing 100 hour weeks I believe) and then pulling back to something more reasonable (or not.) Sure, it might not be sustainable in the long run - but hell, life in general isn't sustainable in the long run. Sometimes you gotta chase those dreams, regardless of the cost.
I consider working on my start-up to be something I do because I enjoy it, not because of external pressures. Building a tech business is just a very enjoyable way to pass the time. I'd be doing that even if I had $100m in the bank.