Actually, sleep is good for you - your memory at least. Various studies released during the last few years have shown that people who sleep after learning something have better recall of the learned thing than those who do not get as much sleep.
In one experiment by Harvard Medical School, 24 test subjects were presented with diagonal bars flashed on a horizontally striped computer screen for 1/60th of a second. Over the course of a day, they were taught to identify the orientation of those bars. That night, half of the participants were allowed to sleep, while the other 12 were kept awake until the second night. All 24 were allowed to sleep on nights 2 and 3. On day 4, the groups were tested on their ability to perform the task. The group that slept on night 1 showed marked improvement, where the group that was deprived of sleep exhibited no improvement.
The researchers concluded that sleep gives your brain time to determine what information is needed and kept, and what can be thrown away. The brain then strengthens and consolidates the connections that form the retained information.
Sleep is like defragging your brain.