Windows 8 Pro x 64. BSOD every few hours with Free Avast installed. DRIVER_IRQL_NOT_LESS_OR_EQUAL BSOD. Uninstalled Avast. No BSOD since using Windows Defender.
Also, when I was installing 8, my free trial of Avast Pro 7 suddenly expired. That was the first sign I had of a problem. Eventually uninstalled AVP 7 and reinstalled Free Avast, which led to the aforementioned BSOD.