My laptop was ventilating loud like half of a vacuum cleaner almost all the time before, especially at weird moments like running idle waiting for input on a command line... It was time to handle. I disassembled it completely, removed a 2 mm accumulated dense pack of dust between fan and heatsink and almost laundried the heatsink to get it totally clean. Aditionnally I mounted a resistor into the fan cable that makes the fan turn about 6 times slower and then I underclocked the cpu to 1.6 GHz via scaling_max_freq and undervolted it using linux-PHC (phc_vid 0 for 1.6 GHz runs just fine).
Now my laptop stays cool (65.0 - 68.0 °C while running boinc applications vs. 60-70 when idle before). Also I can now finally feel the heat flow out of the ventilation holes on the side whereas before it was damn ventilating but nothing came out. And the most important of all: My laptop is now almost totally quiet!! (Actually now, and only if I really pay attention I can hear the hard disk louder than the fan, ^^ to tell you how quiet it is. Everything just like in a new laptop right out of the package! (Before all the cooling problems eventually occur there. ^^))
So a great thanks to the linux-PHC team! This is a really great job. I'm so happy!

The technical details:
hp 6820s laptop with T7250 2 GHz processor (double core)
Running Ubuntu Karmic 10.04 amd64, kernel 2.6.32 and linux-PHC 0.3.2-10 (Still uncomfortable about having to compile kernel 2.6.35 in Ubuntu Maverick by myself, and adding all Ubuntu and linux-PHC patches manually. And I heard otherwise it won't work. But let's take a look at it some time later.)
Cheers