Many people opt for credit cards with rewards, the most common of which are airline miles. We like the idea of shopping for toilet paper at Costco and earning miles for a vacation. But the thing is, according to Bankrate.com, most people never actually cash in their miles. A recent survey shows that 70 percent of airline miles accrued are left unused. When you factor in the unlikelihood that you actually will take a trip within the time frame in which your miles are valid (because, let's face it, trips cost more than just airfare) and weigh that against the yearly fee the credit card company charges, it becomes clear that justifying your purchase for points (or paying with a credit card rather than cash you actually have) is an elusive dream, one that belongs in fantasyland.