If you have a job for which you are paid with a salary, your boss should make reasonable attempts to compensate you when you work well over 40 hours a week (either in time off or money). To be clear: if you work about 45 hours in a busy week, I think it's okay to let that slide if you must do it to get your job done. Outside of that, I don't think employers should be getting much more than about 40-45 hours a week of work from salaried employees. Unless of course you were hired with the understanding that your job would require more than 40 hours of work per week.
I think this is a very ignorant thing to do and I would like to see it stop. I believe opposition to this idea is mainly from interested bosses and workers who have an exaggerated interpretation of what good work ethic means because they are ambitious.