My Asus P8Z77-V Pro has two CPU fan headers.
I completely disabled the "optional" CPU fan alert, (Because I'm not using one now) and turned down the min RPM on the other CPU fan. (Turned down the rpm at which the MB will throw an error.)
So, if my CPU fan dies, (zero RPM) I will get an alert. But I won't be bothered when the fan idles at ~400-500 RPM. (I set the min to 200RPM IIRC)