i basically leave my comnputer on all of the time, unless its been on for a while and i notice a lag in performance. i dont know, it's just that i'm a very impatient person and i hate to have to wait for my computer to turn on. i dont have any antivirus or antispyware aoftware installed, although i prbably should lol. i never defrag unless i have absolutely nothing to do. my computer has probably been on for about 3 months straight and i havent noticed any change in performance.