My tip is to use a thermal compound such as ThreadEasy or its equal, commonly used in the transfer of heat generated by disk brake assemblies, which will transfer heat from your CPU to its heat sink with greater effiency and as a side benefit, it will not dry out in the same manner that the Radio Shack compound does."
I guess people should use something before they comment on it."
I have found that regardless of the maker of heatsink compound it will all "dry out" if subjected to *enough* heat. TO-220 devices (a common case style) are very prone to this, aggravated by running the device/heatsink at elevated temperatures. The hotter the device the faster the grease will bake out. But this is not something to worry about, as the grease is only there to allow the compound to be spread on the device and heatsink junction.
The white stuff is Zinc Oxide (ZnO) and the effectiveness does not seam to decrease with the grease gone.
On several occasions I cleaned and reapplied new compound after changing one device on a heatsink and found that the new compound did not improve cooling. Unless the junction is disturbed, drying out does not look to be a major problem. It might be an indication that more air flow is needed to keep the CPU/heatsink cooler.
There are other heatsink compounds that are much better at moving heat: see this Overclockers.com page. These guys are serious about cooling! Unless one is overclocking or using an early Cyrix CPU, exotic cooling should not be an issue.
After all, most of us are not going to keep a CPU for (more than) 5 or 10 years.
I like to move lots of air through my PC case. I worry more about heat effecting hard drive life then CPU life. Most cases do not move nearly enough air across the HD/CD/DVD area. And modern video boards can also benefit from better air flow.
I found that by gutting a fan, removing the blade, armature and support arms, and using this to space a fan away from the small inlet vent holes, will reduce fan noise (in my case checked with a Radio Shack Sound Meter) by about 9 dB. That is a big improvement in overall noise level. I am using a large (4.5") fan that was just too noisy for comfort. I sacrificed a dead fan for the project. Smaller fans will experience a similar level of improvement."