the longest time I spent awake was 50 hours and after that I just wanted to sleep so nothing bad would happen to me.
My XP:
at about the 20th hour I was a bit wary...I couldn't sleep because of too much energy drinks so I just wandered around. It was quite difficult because my body wanted to fall asleep but it couldn't after several hours this passed.
I spent several hours playing SingStar (which means also reading a text...). Reading wasn't a problem at that time or at least not a text of that size. Worse was looking at the screen all the time as it made my eyes hurt and sometimes I got a nausea feeling.
Several hours later. (around my 32th hour) I played Dance Dance Revolution (actually ITG) and I haven't got a problem passing tenfooters and eleven footers (even though I though it would kill me, because I haven't eaten much nor slept).
This quite demanding physical exercise woke me up and I was quite alright for another several hours.
but at home I had problems with reading, I got a problem with the the flow of time (ehm..I know how the time passes....even when I sleep if I don't black out...) but after 40 hours without sleep it becomes a bit difficult to follow. (it's like time dilatation).
Also my brain has much slower reactions and does not think that fast as it usually does. I'm more open to nonsense jokes or other nonsense.
My body was moving slower (but I could still play DDR without a problem) and was quite lazy.

that's it... I think that it wasn't harmful to me at all. just my memory had a problem...I had to "save" a longer period of time than usual.