The thing is that any thermal paste will do the job but it is just how well it will work. If you only want to run at stock speeds and are not trying to run programs that will stress the system out then the standard silicon grease will do. If however you want to overclock and use things like Prime95 and IBT or run heavy number cruching all day then you will appreciate the benefits of a top quality TIM.
Interesting comments by many here on the subject of thermal paste...
I would venture to say all TIM's are definitely not equal. In fact, as you look at the following charts you can clearly see there are many differences such as the material they are made of, the viscosity, and the temps.
I like the following website because it shows you nearly every TIM know to mankind [well, at least up until 2009]!
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=150&Itemid=62I cut and pasted the benchmarks from the low/top performers. There are also many that fall in-between.
Hope this helps!
Soar
PS Keep in mind, Arctic Silver 5 Polysynthetic Thermal Compound requires up to 200-hours recommended curing time!!!