Thirty years ago the airlines created a marketing program that has been hugely popular and successful—frequent-flier programs. But today, with high fuel costs and airlines seeking every avenue available to offset them, the frequent-flier programs are not exempt. Carriers, including American, Continental, Delta, and United, have all made changes in their programs regarding frequent-flier mile usage. Changes range from increasing the number of miles required for a free flight or upgrade, adding a fee of as much as USD $100 for usage, requiring a co-pay of as much as USD $500 to acquire an upgrade, and designating some seats unavailable for program usage.
These changes, coupled with the carriers cutting of route networks and seating capacity, make the once highly valued loyalty programs less desirable. However, miles earned by flying are still the only ones that count toward elite airline status recognition and upgrades.
Source: msnbc.msn.com