I've no idea about long term, but these were the short term effects of my sleep deprivation:
* I no longer cared/needed sleep, i was just content to stay awake for the sake of it.
*However, once I reached this state, I puked about 5 times, and my mouth tasted like pure caffeine.
* I went through a couple of hours just laughing at everything, I.E. my friend sneezed, I laughed, my mate went to the toilet, I nearly fell over laughing.
* Incredibly horny, I would have actually boned whatever someone had put in front of me, but that may have just been the two incredibly hot girls that stayed up with me.