At one of my first jobs out of college, the Senior VP of my department always left at the same time every day, I believe it was 5:30. On a number of occasions I heard his boss and his peers comment on this; something like "Of course he's not here, it's 5:45."
I finally brought the topic up with him one day and he very confidently told me that anyone he's ever worked with or worked for knows his philosophy. Eight and a half hours is a long time. If I can't get my work done in eight and a half hours, there's something wrong. Sometimes it could be the organization, but most likely it's because I'm doing something wrong. Either way, I fix it, and I can get everything that needs to get done in the time it's supposed to take.
I thought about this for quite some time, and also observed him. I realized that he was extremely hard-working and efficient. He never goofed off, and rarely spent any time during the day doing anything but work. An hour before his leave time, he would always make sure he'd returned every phone call he needed to, and he checked in with each and every person who reported to him to make sure there wasn't anything urgent that needed to be taken care of.