It depend whether your fan is temperature sensitive or not.
If your PC is, it will make the fan run faster or come on more often as your cpu is running 100% all the time instead of just as needed, my laptop fan runs alot more, but I just throttle down the cpu at night a little to keep the fan from coming on.
One good side to this for anyone wanting to overclock, is burning in your cpu using a cpu intensive program like UD or seti can help produce better overclockability!
