I have done a bit of not sleeping, so I can share my experience.
I can do two days of work straight, with the help of coffee, and suffer no ill effects. As long as you eat regularly (every 3-4 hours), and have stimulants like music going, it's doable.
My speech and reflexes slow down around the end of the second day. Also, I can no longer produce quality anything, but can read books, surf the net, and watch TV just fine.
Third day is tough and almost any kind of a comfortable chair or a semi-reclining position will get you to sleep. This is when I usually clock out, sleeping in my chair at work. It's really funny because apparently I sleep upright with my hands on my laptop, and it looks like I'm still working.
I start hearing auditory hallucinations past 60 hour mark. Really weird, like whispers and radio static.
I never took it past 3 sleepless days in a row because, apparently, you get a bit of permanent brain damage at that mark -- something that has to do with memory. It's not good for you body either.