Well, my buddy would tell you to turn it off now! He used to leave his on "Truck Driver" until one night he came home and the Processor fan had stopped and his 2.4 P4 processor did a melt down. I personally think the risk of a fan stopping are something else happening when you leave it on are greater than the risk of cold starts. I have been cold starting my different PC's since my IBM 8088 many years ago to my 2.4 P4 today with no problems, I really think these posts are as mine personal opinions from each persons experience, even if it fried the motherboard from a cold start rush or something like that my buddy could have bought a nice Motherboard for $229.00 what he paid to replace his P4. Me personally I'll take the cold start risk were at least if a fan stops or something is overheating your there to deal with it because your PC will let you know by some sort of malfunction shutdown,lock-up,etc. Bottom line I would just use common sense if your PC is brand new and with a warranty leave it on if it's a few years old never been cleaned a million dust bunnies your gambling