Well most of us are well aware of this problem. This is my third dell and one of the prime reasons for changing my system other than the hardware upgrade was heating of the system. Little did I know the fix was not that hard at all. In fact a couple of months ago I was again thinking of an upgrade to dell latitude. But then one of my friends suggested that it was the dust that had accumulated near the heat sink and that is the reason. I had ripped up my laptop before to upgrade the hard disk but then I never saw much dust layer on the mother board or the top of the fan that could cause the issue. But had to give it a shot so I decided to open it up again. Well this time also I didnt see much of dust on the fan and then I decided to open the fan least there may be something. And viola there was a thick layer of dust betwen the fan and the heat sink. This was the only issue that was causing the heating problem. I neatly removed the dust layer and cleaned the fan and sink with a cotton bulb. I replaced the fan and put together the parts. I was amazed to see that there was no heating at all and it was as if I had bought the comp when it was new. Added adavatage was the battery life also increased as there was less heating. So there lies the solution if you feel your dell laptop is getting heated up beyond rekoning as it grows a year or so old then try taking it to some service center and ask cleaning then up the heat sink and the fan. Or if you are enthusiastic try ripping it apart and clean it yourself. Just one piece of advice download the datasheet for opening the laptop before you proceed else you might curse the moment you took the decision of opening it up.
Hope this article will help some of you to save money and keeping faith in dell.
PS. you might want to use a tooth brush to clean the vent of the heat sink