More than 45 million frequent-flier credit cards have been in circulation for the last three years, according to the Nilson Report, a payments systems newsletter.The problem is that the frequent flier miles consumers rack up each time they use their credit card aren't worth nearly what they were a few years ago, and the airlines' financial problems are making them worth even less. While people are sure to bemoan the losses and new hassles that come with redeeming their accumulated frequent flier miles, what they really should be doing is looking for a new credit card. Credit cards offer a number of advantages and disadvantages, depending on how you use them. (Don't miss " 10 Reasons You Need a Credit Card" and " 10 Reasons to Avoid Credit Cards") If you have learned to pay off your credit card balance in full each month, taking advantage of the perks that credit cards offer is a great way to do your shopping. Airline frequent flier miles reward cards have been a favorite for many years with people earning a mile for each dollar they spend. When you look at what you get these days, however, it's likely that you could do better by switching to another type of reward credit card that more closely matches your spending habits. Here are some of the reasons why. 1. Fewer Seats Available As airline fuel prices have increased, airlines have been looking for any way possible to cut expenses. One of the ways they have done this is by cancelling flights. The result is fewer flights that are more crowded and have fewer seats available for those trying to use their accumulated frequent flier miles. All those miles are not worth anything if you are not able to redeem them for the airline ticket you want because there are no seats available.