The CPU, specifically Sandy Bridge models, deteriorate if the voltage is too high, if the BCLK is too high, or the clock speed is too high for too long. If you are getting temps of 90C and higher, and leave the computer as such temps for hours, that CPU will almost certainly deteriorate as a result of such high temps burning the silicon. If you can keep your temps under 90C, you are in good shape, although most people, mostly enthusiasts or overclockers looking for attention/bragging rights will want temps as low as possible (which they'll do by buying expensive coolers). I like my temps under 70C because I believe OCing can damage the CPU and keeping the temps as low as possible only prolongs the CPU's life. It's like buying a car with a supercharger installed, you really don't need it to get to work everyday, but it's nice to have in working order.