American Airlines established the first frequent-flyer program in 1981, and for years it seemed like nothing but a win-win situation for passengers: earn points for every mile you fly and, once you've accumulated enough (generally 25,000 miles for domestic flights), redeem them for a free round-trip. Except that those flights are getting less and less free. The airlines now charge for booking within an arbitrarily set time period (usually 21 days before your flight), booking over the phone or restoring mileage for flights that you wind up not using. Worse, the supply of frequent-flyer seats is limited, and in heavy travel periods (like, um, this entire summer) they're almost nonexistent. Unless, of course, you're willing to spend double the miles.