My experience in talking with people who have successfully grown startups to medium to large sizes is that they almost universally regret their former belief that the degree to which they worked hard was necessary to get the company to that stage. From my own experience growing a firm from nothing to a profitable low seven figures sales a year, I would agree.
I know that at the beginning I felt that my talent and experience was absolutely vital to the firm's growth. That if I did not put in that extra hour, I was robbing the company of its potential future.
The reality is that I am not that smart and not that talented. Much more important than running around personally implementing everything is growing a group of effective managers who take pride in their work and whom you can trust in running your business.
I think a weakness in many internet businesses (certainly not all of them though) is that because they are so little focused on revenue, it becomes necessary to either (a) try to implement everything yourself, thereby saving labor costs, or (b) spend tons of time raising money (and destroying your ownership in the process), which deducts from time you can spend selecting and growing your managers.
The first time I felt I realized I could leave my company for a week with no cell phone, no BlackBerry, no Internet access, and not be terrified of what would happen -- it was a huge relief, and that was when I began seeing the folly of my ways. It's not about me, it's about my wonderful managers. Working obscene hours is not the way to do that.
Of course, you shouldn't be a slacker either -- people do take cues from you -- but as others have suggested it is far more important to develop your firm's talent than to try to do everything yourself.