A colleague of mine had some problems with very high temperatures in a laptop. The temperatures was about 71 degrees Celsius at idle and 91 degrees Celsius a full load. (It was a HP laptop with some kind of dual core). I opened the laptop up and took out the fan. In the space between the outlet of the fan and the heat pipe there was a rather thick layer of dust. I cleaned it and now the temperatures where about 5 degrees lower.
I my colleague's case there is probably something else wrong with the fan (or computer), but it is clear that a little bit of dust defensively can have an effect on the temperature (and sound level).