Actually, it does matter how much thermal compound you use. You should apply enough to cover the top of the chips, but not enough to be squeezed out by the pressure of the heatsink clamps. This is vital, because too much thermal compound can cause problems due to the fact that it is conductive, and if it comes into contact with chips on the motherboard, you can end up with a $300 paperweight. Just recently, I repaired a RROD Xbox 360, that already had an attempted fix, but had thermal compound oozing out under the heatsinks, so doing it right is important.