Many people do not know what the thermal goo is for. If you look at the surface of the heatsink and CPU (the chip that's sticking out), you may think that it's flat, but under a microscope, there's millions of hills and valleys. The problem with these valleys is that they do not make contact and therefore traps air. Air isn't a very good thermal conductor. Therefore, the thermal goo is used to fill these valleys and get rid of these gaps. You should use as thin a layer of Artic Silver or whatever, and not put so much that the CPU is actually floating on a layer of the substance. If you want to know if you're putting too much, remove the heatsink after applying and look for the extra goo that's pressed out at the sides. Stuff that's pressed out is wasted, so try to put less next time. As a guide, use about 4-5 times the white stuff that you press out of your pimples on your forehead. I'm talking about the average pimple, and not the volcanic ones. 😀