As we head into the holiday shopping rush, you'll notice retailers turning up the heat with sexy new credit card offers. "Sign up today and get 20% off your purchase!" "Instant savings at the register ...

You know the pitch. You're at the checkout counter, and the cashier says, "Want to save 20% today by opening a store card?" I've fallen for it in the past at Macy's. And regretted it later when the ...