I reliably put in four or five 50+ hour weeks per year (especially if I'm at a new startup), but I've learned through hard experience that it's unbelievably counterproductive to do that for longer than a week or two at a time. My personal life and ability to stay awake, much less think/code clearly, suffer otherwise.

Of course, if work is sufficiently interesting then I end up spending what free time I have thinking about it, which can make my work time incredibly productive, obviating the need to be "working" too much to begin with.

But most importantly: YMMV.