Joining FF programs are free. however don't become penny wise and pound foolish. Many people will fly XXX airline because they want to rack up the miles on that airline even if BBB airline has a much cheaper fare. Unless the difference is neglible I would recommend for the casual flyer to always fly the cheapest airline. I am a very frequent flyer with Continental and have attained Platinum elite status because I fly so much for work. I average 100,000 actual flight miles flown. I earn lots of bonuses and such because of my elite status and yes it is worth it to me to sometimes fly Continental even when they are not the cheapest because I will accrue many more FF miles because I chose to fly CO. For example flying New Orleans to Singapore is over 10,000 flight miles one way . If I were to fly United (where I have no status) I would only earn the 20,000 miles (10K * 2). However if I fly CO for $100 more I would earn 45,000 FF miles because CO awards their Platinum elites 125% mileage bonus. I earn 25,000 additional miles just for flying CO.