I have to shut i down every night because I canīt sleep with it on, to hot and to mush noise.
well the longest period of time i had it on would be about 72 hours straight, but then I sat in front of it all the time... lan-party.
I have friends who have their computers on for up to 3 month in a raw and then they restart and keep going in a few month more until next restart... they have been doing so for the last 5 years
... and they havīnt changed parts in their comp during that time. the thing that can break is the hard-drives... to many rotations.