I have had a Dell Latitude D830 laptop for the past couple of years. Core2 Duo, 2.5 Ghz, 4GB RAM, Vista64. In the beginning it was flying. Fastest computer I have ever had. But then as the months went by, it started to slow. Recently, performance has been horrible. Looking at the system resource, memory was OK. But sometimes in Visual Studio I had to wait for the IDE to catch up with what I had typed (running Firefox with 20 tabs, Visual Studio 2008, Outlook, Excel and Sql Management Studio, but I used to have no problem with all of them open at the same time).
After some Googling, I saw that the first thing to check in my case would be the system temperature. If the system is overheating then the processors cant run to their full potential. And lo and behold, when I lifted up the laptop, there was dust all over the Fan intake (and the laptop was so close to the desk that even with it clean hardly any air would get in). So I cleaned off the desk and underside of the laptop, and propped up the back of the computer (I knew that I would get some good use out of this). Downloaded and installed Speed Fan and watched all of the core temperature numbers drop. Computer performance immediately went up. (I also took off the keyboard and checked to see if there was a buildup of dust inside the fan, but it was clean. Ran the fan diagnostic and it was ok as well). The computer is still running hot (still something to work on), but I have definitely learned my lesson – high performance laptops really suffer in the heat. Keep them cool!