There is a sticky at the very top of the Cooler and Heatsink section of this forum about lapping a heatsink and cpu:http://www.tomshardware.com/forum/252168-29-heatsink-lapping-guides
I lapped my 120 and an AMD cpu. I did not need to do it. I just did it to see if I could. My cpu core temperatures dropped a little bit less than 2C after lapping. Other veterans report similar results. Sometimes temperatures do not drop.
For the typical user or gamer it is not worth doing. A temperature drop of 2C is insignificant. In addition, lapping will void the cpu and hetasink warranties. It might make a difference for an ultra hardcore gamer or enthusiast into very serious overclocking.