Perhaps nothing drives home the reason behind the apparent scarcity of award seats as well as a look at the numbers: According to Randy Petersen, editor of InsideFlyer magazine, there were 180 million members of frequent-flier programs worldwide at the start of 2006, sitting on almost 10 trillion unused miles. That's more miles than there are stars in the Milky Way (about 100 million), people on earth (6 billion), or U.S. pennies in circulation (8.23 billion in 2006). And it's about 200 million free flights across the Atlantic or Pacific—at least theoretically. "There is record mileage and a limited supply of seats," says Matthew Bennett, editor and founder of FirstClassFlyer.com. "Whether the supply is shrinking or not is debatable. But either way, it's a no-win situation."

Petersen is more blunt: "There are some programs that are really, really good, and some that are really, really bad. No one wants to think about whether they're a member of a bad program." (Visit Petersen's webflyer.com and click on "Ratings and Reviews" for a comprehensive list of programs and how he and other travelers think they stack up.)

How to Play the Game
Most elite-level members of frequent-flier programs are well versed in the best ways to use their miles. But for the rest of us, the difficulty is in deciding how to play the game: Do you go for an award ticket or purchase a seat in coach and use miles to upgrade to business or first class? What about cashing in miles for a premium-class ticket? Our survey found that nearly 70 percent of readers use their miles for free tickets, as opposed to the 27 percent who use them for upgrades.

But based on airline ticket prices—which for business or first class can be more than ten times that of economy—you'll often get a better per-mile value by upgrading than by redeeming miles for a ticket, particularly on long-haul international flights. Winship notes that domestic first class is often vastly inferior to international first- and business-class service, so remember to consider whether you're willing to sacrifice a sizable number of miles for a little more legroom and a larger seat on a domestic flight.

Depending on how the miles are earned (by flying, through purchases, etc.) and how they're used (for upgrades or free tickets, or even redeemed for merchandise), they can be worth anywhere from a penny to 8 cents. But experts put the average value of a mile at about 1.2 cents. Keeping that in mind, you can determine whether it makes sense to cash in miles for a ticket by multiplying the number of miles required by 1.2. For instance, cashing in 25,000 miles for a ticket that you could purchase for $300 is not a good deal, since you'd just break even, whereas redeeming 120,000 miles for a business-class ticket valued at $5,000 is an excellent value because you'd be "buying" the seat for the equivalent of just $1,440.