Once you register, for example, on UA's www.mileageplusshopping.com you'll get the occasional email with promo offers, however, it's not all inclusive. If you're looking for a deal, like most of us are this time of the year, the only way to guarantee that you'll catch a promo is to login to the portal daily and see which retailers have that little slash through the bonus miles/points and see the temporary rate increase.