TestFreaks posted a guide about optimize your computer for speed and efficiency

I've been into computers for many years now, too many to count at this point, but when someone in my family or any friends have a computer problem they call me to help them out. One of the biggest complaints I run across is speed, and why is their computer running slow. There are of course a plethora of reasons their computer is running slow, usually it's a virus or they've just got too much stuff going on at the same time and their computerjust can't handle it. Another thing I've run across is that people think a five year old computer should be able to do everything that a one year old computer can do, they think if it's not broke, don't fix it. Generally that's a good rule, but not for computers really, the technology evolves so fast that in about six months your brand new computer is now a generation or two behind what's on the market today. There are several things that one can do to make their computer faster and more responsive and I've compiled a list of many of them, it's by no means every single thing you can do, but a lot of them are ones that the average user can do themselves with little or no technical knowledge. These tips are not limited to desktops, but for netbooks and laptops as well, but they can be limited by the operating system you're using

Tips and Tricks: Optimize Your Computer For Speed and Efficiency