I watched a program about sleep disorders and stuff. They say there are close to developing drugs that will keep you awake, with no side affects of tiredness etc. Apparently, physically your body doesn't need to sleep. So long as you rest, it can continue to heal and do fine without sleep.
Your brain on the other hand will turn to mush and you will DIE.

Sleep is important for physical recovery as you aint moving, but mostly it's for psychological recovery. While you sleep, your sub concious process all the information, sorts out your stress etc etc blah blah (hence dreams). This is why when you 'sleep on it' you wake up feeling better about things the next day.
So one day we'll be able to take drugs that keep us awake indefinitely, without symptoms of tiredness, but if we abuse them, we will go mental, put tea coseys on our heads, drool, start muttering 'Wibble' constantly, and eventually stab each other to death.
I vote for sleep.