[Guy_Kuo]

Given the now documented propensity of some MacBooks to melt the insulation of a thermal sensor wire and develop random, intermittent shutdowns after a month or two of normal usage, I think it advisable for all MacBook owners to test their machines and expose any weakness while it is WITHIN warranty. A newly purchased MacBook probably should be thermal stress tested well before the 14 day replacement period expires.
Opening terminal and running yes in two windows maximizes CPU utilization and temperature. Several overnight runs or a 24 hour run without arranging extra ventilation should expose any MacBooks that are physically prone to melting their thermal sensor wire insulation. The goal of the run is to heat the heatsink to as high a temperature as it will ever experience and hold it there for several hours. If the insulation holds, it should continue to do so. If it melts, the machine will start experiencing intermittent shutdowns during normal use.
A few days of normal usage after that session would give good peace of mind that the machine is less likely to fail later. Intentionally thermal testing early gives owners a better chance to have a fault prone machine repaired under warranty or replaced.
This would also be useful for newly repaired MacBooks prior to putting them back into critical usage.

[MacCheetah3]

Hi
I did this already but not purposely. I've been re-encoding DVDs into H.264 for archiving and one time had my machine doing so for about 7 hours straight overnight. This process maximizes CPU and RAM usage and therefore the fans start 'cranking'.
No problems yet, except for the whine I need to take care of yet. It hasn't really bothered me much yet but I want to take care of it for that day of when I sell it and just because.