Overclocking voids warranty because you force the hardware to work harder than the manufacturer's specifications, the optimal operating level, thus risking the hardware to fail and shortened it's lifespan. So overclock at your own risk.
I'll believe that when I see it. It only "shortens lifespan" when some dumbass puts 1.8v through it on a stock cooler. Also, it IS possible to detect higher than normal frequencies on a chip by seeing how much stress has been placed on the Silicon. Yes, it can be done. However, CPU's fail so little it's highly unlikely it will break, and even if it does, you can return it to a place like Newegg that has NO way of knowing what you did to it.