Re: What is the PerfLevelSrc hack ?
Although I don't actually know what its purpose is, one of the side effects of the tweak is that it causes your GPU to be at max speed at all times (rather than ramping up on demand). That causes the GPU to become much hotter and, if you are using a laptop with poor cooling/blocked air vents/dirty fans/non-functioning fans/etc, yes, it would certainly shorten the life of the laptop.
I recently did a massive cleaning on my laptop and the average idle temp while using compiz and the tweak dropped about 20C. If you use the hack, make sure to at least use some compressed air on your laptops vents fairly regularly (once a month should do it depending on the environment). It makes a huge difference.