Always remember to remove the plastic from the bottom of the heatsink, before locking it onto the processor. It greatly increases how well the thermal gel works.
Mom reported to me this weekend that the computer I built them for Christmas was shutting itself off. I messed around with it a little bit yesterday, turned on the ASUS probe software, and saw it was running a little warmer than I thought it should. Like 48C just idling. Started surfing the web and quickly got a siren going off, because the temp was up to 55C. With the handy clear side I could see all the fans were running, so I thought maybe the stock thermal gel had dried up or something. Not a problem I've had before, but hey who knows. Popped the side off, removed the heatsink, and found that darn plastic piece there. I was right in the fact that the stock thermal gel had dried up. Drove 30 miles to Radio Shack for some artic silver 5 to fix it. Now with a heavier load on it, SpyBot S&D searching, AVG scanning, Open Office 3 Writer open, and surfing the warmest temp I've seen is 45C. Was idling in the mid 30s.