Way back in the mists of time, 8 months in my second job as a programmer, we had to replace an existing payroll system with a new one for a very large corporation. Looking back, I know the project management on that was abysmal, but I knew nothing of that then - just that we had to put the new system in place and stress test it in one shot, during a long weekend.
The days leading up to this were themselves 18 hours long, but that Tuesday, a dozen of us stayed back at work, and did not go home till the next Monday. We slept intermittently, heads on keyboards. I remember one time my boss was going over some logic with me, and I was nodding off while he talked. He paused, looked at me, and said - "How about you go and wash your face and come back. We really need to complete this one now." That week I logged in 150 hours D:, and the OT was a pittance.
The upgrade went off okay, mostly, but with not much reward for us. In fact, a senior VP called us in a week later and said that a glitch had been identified and wanted to find a scapegoat for it, but we were too pissed to give him one. My mom says I lost 10 pounds that week.
I was in that nasty job for a couple of years, where long days were a regular thing, but mostly because I met my wife there and wanted to close that deal before quitting . (She was in a better department, and remembers that place fondly...)