If it was up to me, I would probably leave my PC on 24/7(can't seem to convince my folks that a PC in idle doesn't take much juice). I agree that turning a PC on/off all the time isn't good for it. The expansion and contraction of a PC's hardware by constantly powering up and shutting down might affect the lifespan of these components(especially HDDs). The PC On/Off debate will always be subject for discussion... I guess I will stick to my opinion and say "always On" is better.