As reported earlier this week on INflightOUT, American Airlines, following the lead of other airlines, began requiring timely activity to member frequent-flier accounts. Failure to comply means fliers risk loosing everything they accrued in their pot-0-miles.
Airlines no longer want to keep "old" miles on the books. If you flew to Europe in 1999 and earned no other frequent-flier miles in your account since, the airline wants to drop your account off its books. Those unredeemed frequent-flier miles represent a debt to the airline, much like an undeposited check. The miles and check both go "stale" after a while.
"Stale" miles equate to zero value nowadays. Depending on the airline, miles are forfeited for inactivity of 12-36 months. Don't let the miles go stale!
Any qualifying activity usually keeps those miles fresh. Back in the day, airlines required you to FLY to earn frequent-flier miles - ha, long-passed are those days. Today, you don't even have to visit an airport to earn airline miles. For example, you can earn miles for grocery shopping, video rentals, dry-cleaning, credit cards, school tuition, and car rentals, to name a few. Visit your airline's frequent-flier page, then click on the section detailing how to earn miles from other than flying.
Use'em or loose'em!