I used to replace my computer about every three years but found that when hard drives started exceeding 100GB, 500mb RAM, and 2.4Ghz Pentiums came around that they finally hit a speed and capacity that the average user needs could be satisfied. Now I am not into the gaming, don't visit the porn sites and have no desire to watch TV on the computer so this last unit I built in 2002 is still running AOK. Mind you I went with quality motherboard, CPU, etc...and turn the PC off when I am not using it. So in six years I have formatted and reloaded the OS just once. I did buy a pair of hard drives since they don't sell the 120GB Maxtor SATA drives anymore. My 17 inch monster CRT which I bought for a steal for $500.00 when they were first new now sits downstairs and is used only to setup new PC's. I did upgrade to 17 inch BenQ LCD several years ago. I guess it depends what you use the computer for and how you use it that plays a big part in how often it should be reloaded.