Looking at actual temperatures at intelmactemp.com for various people's MBP 2.0's, I can see that the average core temperature under load is about 80 C, with a standard deviation of about 7.5. The range of temperatures is 34 degrees.
What this means, unfortunately, is that your experiment tells us NOTHING about what happened to your computer because of the thermal paste. For example, assuming that your computer and your friend's computer were both within the middle 68% of computers, then applying the grease might have INCREASED the temperature of your core by about 14 degrees or DECREASED the temperature of your core by 18 degrees. If your computers were unusual, then those numbers would be even larger.
I'm really happy that people are trying to get to the bottom of this, but for others who try, I want to stress the importance of taking before and after measurements. Without these measurements, there is no way to determine what happened.
Let me give another example. Let's say I wanted to see if drinking some ice water lowered my body temperature. To do this, I drank some water, then compared my core temperature to my girlfriend's core temperature. Of course, this tells me nothing because we I might normally be either half a degree cooler or hotter than she is (actually I am slightly hotter than she is).