But some other airlines have had less than stellar success with experiments. American made a big public-relations splash in 2000 with its decision to take out seats and add more legroom. Now, it's not only reversed that decision, but it also recently announced it was taking pillows off some short-haul flights to save on the cost of cleaning them.

"When we do our customer research, they say their first priority is a low airfare," says Tim Wagner, an American spokesman. "The other things they may value to some extent, but not to the extent that they want them if they'll end up raising the price."

But others like Clint Oster, an aviation expert at the University of Indiana at Bloomington, see it differently. "That's one example of some of the experimentation that's been mindless," he says.

Some of American's customers have noticed the changes, and they're not pleased. Political blogger Bryan Keefer usually flies JetBlue from New York to San Francisco to see his family. But last weekend, he decided to use up some frequent-flier miles and took an American flight.

"I certainly didn't have any extra legroom, and I used to like to fly American because of it," he said shortly after touching down at Kennedy Airport on Sunday night. He also thinks the overall service has deteriorated: He says it took far too long for the flight attendants to remove meal trays. Then, because half of the reading lights on the plane didn't work, the pilot turned on the overhead lights during the movie, which annoyed many people.

So, despite having racked up quite a few frequent-flier miles on American, Mr. Keefer says he'd prefer to fly JetBlue because the planes are more comfortable and "noticeably quieter."