I turn of my PC because it is so freaking loud, I am getting a water cooling kit/system installed soon, and it has actually been off for a while (not been doing much PC gaming, a lot of WoW on the Mac) but I watch movies on my iMac to put me to sleep so it usually is on overnight and don't get worried about the DVD menu getting burned into the LCD, i usually wake up when it ends (not on purpose just a body habit thing) to turn the screen saver on. But that's it.
I just can't sleep with that PC on being as loud as it is and espically because it is right next to my head, because the desk is right there.