My one pc has been on for over 3 years and no problems. My new compaq has been on since i got it (3 months back). My computers are on all the time. I only turn them off if there is going to be a BIG storm. Outher wise they are on all the time. Now if you have a laptop. i recomend that you turn it off or put it in stand by when you are not useing it. But a desktop leave it on all the time day and night. But id reboot it every day or every outher day.
Used to leave our 2 machine on 24/7 but it was costing us a fortune in electric. Since we've started turning them off at night and when we go out we've more than halved our bill!
Anyways, I usually leave my computer on from when I get home from school to when I go to bed. It's near silent anyways so it doesn't really bother me. If i really want to, I can leave it on overnight without it disturbing me.
I'd say I wouldn't do so. Hard drives can go bad after running and getting close to its max hours of life as well as with fans and such. I turn my computer off every night.
24/7 on my desktop because I am folding although it isn't for computer forum it is for another forum. and for my laptop i sometimes leave it on for 24 hours a day or just when i am using it and i am also folding with it.
My laptop is always on when(accept when in transport 2 days a week for like 3 hours total) and my pc never is turned off. I restart it about once a week or so just to clean things out and the patches and such.... Both are folding so they are always on doing good for man kind lol!