I'd agree with David that in the short term, on a project or two, the mega hours help you. I've worked overnight on SQL issues at times and I've learned as much from those experiences as months of regular time. Those are invaluable and pack an amazing amount of experience into a short time.

But those work in the short term. Running for a year, or even months like that isn't necessarily good for the health or careers of the people or company. If there's success, then it helps, but if the company fails, invariably there will be plenty of people that feel let down and they will have missed something of life.

It's also a young person's game. Once you have a family, not sure you can make those trade offs and feel good about it.