Holy dust bunnies batman!
I was worried that my CPU temperatures were too high (about 73 C under load on a Phenom II X6 2.8 GHz), I opened up the computer and there was a layer of dust between the heatsink and the CPU fan (not easy to see due to the angles of the fan blades).
I blew the dust out and the temperature under load dropped to around 51 C, more than a 20 C drop just from clearing out dust!
I was thinking of buying some Arctic Silver thermal paste, but I'm going to keep my money now...
My Mario Kart Wii friend code: 2707-1866-0957