I find I can't work at a reasonable pace. Either I'm slacking off, and for all intents look like an incompetent retard, or else, I'm in crisis mode and will do whatever it takes. Unfortunately, after crisis mode, I'm burnt out for a week.
There's an amazing feeling of monastic purity to working no-holds-barred on a problem, though. It's simplifying. No life -- no worries! That and the adrenaline rush of looking into the abyss and then finding some way around, or over.
At the company I work, it's beginning to feel big-companyish. There's around 100 employees now, and the bureaucracy is starting to set in. Despite that, we still get features rolled out at a nice rate, but I really have no emotional connection to the product we make. That doesn't mean I don't do quality work. That just means I'm not as interested as I could be.
On the other hand, if my future depended on the success of my product, then I'd be kickin'. I personally think that even with the stress, the time, the lack of sleep, that it would be one of the most fun experiences of my life, because I'd get to see my product morph from nothing into everything. Totally worth it.
Unfortunately, I have to feed myself, so I can't just quit and run after my idea. But if I manage to scrape even $15k together, I'm doing it.
You should read this article: http://www.doingsuccess.com/article_514.shtml
By the way, what's your startup?
I find myself getting sick after doing this for periods of time. But it's definitely a hard-to-break behavior. I still average 4-5 hours per night.
Can't say I'd take it back for anything. There's probably not a full-time job opportunity in the world that will replace the excitement of being an entrepreneur.