Did Your Boss Thank You For Coding Yourself to Death?
Studies about productivity declines when working more than 40 hours a week surface with disturbing regularity. As a developer your creativity declines, you make more mistakes, you miss existing issue etc., to the point where you're doing more harm than good. Should I even mention the health concerns when you spend that much time engaged in the same activity (they even had rules about spending too much time at work in the Soviet Union, and those guys were all about putting in the time for the good of the people).
more on skorks.com
An excellent article on overtime programming work.