i have worked all sorts of schedules, all of them forcing into not sleeping.
but before i was working 19-20 i used to have to get up at 3am for work and work till 3 pm. from there i did whatever it was that i did till about 8pm and started watching tv and movies till sometime between 10-mid night. on average i was getting 3-4 hours of sleep a night. this was before i cared about nutrition and i did not take any stimulants, even caffeine. sometimes i would make a week or a couple months. then i would hit a wall and crash. i would be able to make it longer during the summer months than the winter months. i would generally go through a lay off during the winter months.
after i started working out and got my nutrition pretty good, i would sleep 4 or less hours a night, for 6 days in a row and sleep most of sunday.
i think it can be done, for long periods of time, but for good i think it would very difficult to do and keep mental awareness.
as you can tell by the rambling i still do not sleep, but i now can not go without, no matter how much caffiene i have had. there is no way i would make it long with a sub 4 hour sleep schedule!