Neil Postman writes:
"Now . . . this" is commonly used on radio and television newscasts to indicate that what one has just heard or seen has no relevance to what one is about to hear or see, or possibly to anything one is ever likely to hear or see. The phrase is a means of acknowledging the fact that the world as mapped by the speeded-up electronic media has no order or meaning and is not to be taken seriously. There is no murder so brutal, no earthquake so devastating, no political blunder so costly--for that matter, no ball score so tantalizing or weather report so threatening--that it cannot be erased from our minds by a newscaster saying, "Now . . . this." The newscaster means that you have thought long enough on the previous matter (approximately forty-five seconds), that you must not be morbidly preoccupied with it (let us say, for ninety seconds), and that you must now give your attention to another fragment of news or a commercial.
(Amusing Ourselves to Death 99)