My November 2010 Dell Precision M6500 began to develop a variety of problems just out of the 3 year warranty. It began to slow down to a crawl especially trying to do anything with big RAW files in Lightroom. The Windows experience Aero graphics score fell from 6.8 when the computer was new down to 2.8. The video drivers on the Dell site for the NVIDEA Quadro FX 2800M graphics card were rather old so I downloaded the latest (Nov 2013) drivers off the NVIDEA site. I also updated to the latest Dell bios. Neither made any difference. The fans began to run all the time. The computer frequently spontaneously rebooted. It suffered several blue screen of deaths. I thought I might have a virus (as the symptoms seemed to have developed quite quickly). Scans with Sophos and Malware bytes revealed nothing and the problem persisted when disconnected from the Internet.
Suspecting overheating I used the online Dell service manual and dismantled the computer. This was the dust on the inside of the CPU heat sink.
This is how it should look. The graphics heatsink was similarly blocked but was even more difficult to get at and clean. No wonder other threads talk of Dell replacing the video card when the computer is still under warranty.
Once back together, the computer is running cool again with hardly any noise from the fans. It is also working like greased lightning and the graphics score is back to 6.8.
It is a real pity that the whole computer needs to be dismantled to get at these heat sinks. It is not a great design. I don't think the above vacuum cleaner trick would be able to suck the dust through the heat sink without disassembly. Even when the heat sink was dismantled, I could not suck the dirt through the heat sink, it had to be blown back the way it had come. If you reversed the vacuum and blew through the assembled computer grill, you would just blow the dust back into the fan and it would subsequently reblock the heat sink.
Perhaps regularly using the vacuum on suction through the computer grilles might prevent the build up of dust, I don't know. Otherwise it is almost inevitable that your Precision M6500 will become affected. It took me about 7 hours plus a trip to Maplin for some heat sink thermal compound paste to get it running again. It is not what I expected from a top end laptop. Perhaps they are built with a three year life expectancy for business but I am a private buyer and expected it to last longer.