Compare the real, out-of-pocket cost of transporting you as a passenger. When you factor in the meal, a little jet fuel, and perhaps the time spent processing your ticket, that free ticket cost a measly $15. Clearly, frequent flier partnerships pay off with huge profit margins.

4. Blame JetBlue and Southwest for the rules changes

With a lot of fanfare, these upstarts came along and essentially slapped time limits on their versions of frequent flier miles. That means, if you don't use hit a certain magic number within a 12-month period and then redeem the miles in for a free ticket, your miles simply expire.

To use industry lingo, JetBlue and Southwest are increasing the "breakage" frequency. You're losing miles almost as quickly as you can rack them up, so these airlines don't worry giving away seats. So unless the passenger is a constant jet setter, this will be a losing proposition.

On the other hand, with older carriers like American, United, or Delta, the rules have always been more generous: The life of a frequent-flier account is automatically extended within a three-year period whenever there is any form of activity within it.

"I learned quickly that those JetBlue miles aren't worth it," says Jay Akasie, an M.B.A. candidate at Columbia University who flies about a half-dozen times a year. "As far as miles programs go, I'd stick with the older carriers any day."

5) When your airline goes bust, don't be so sure your miles won't

The airline industry is mired in a slump, slammed by soaring fuel costs and stiff competition from aggressive discounters.

To be fair, miles don't always vanish. In 2001, when TWA filed for Chapter 11, American Airlines purchased all of its assets, including its "Aviators Program." Members, and their miles, were instantly grand-fathered in.

Regular business travelers on National Airlines, however, weren't so lucky. When the Las Vegas-based airline went kaput in 2000, so did its "National Comps" program. All that customer loyalty was for nothing.

5. Wheeling and dealing miles could get you grounded

Savvy travelers, for business and pleasure, should know it's perfectly acceptable to give a plane ticket earned with frequent flier miles as a gift, as long no money is exchanged.