This is a big problem for the "full service" (e.g. not the lowfare) airlines. Yield management has resulted in increased profits for a while but now the gap between business and leisure fares is so great that with pressures from the down economy, many business travelers are using leisure fares to travel on business. So the airline's pricing models are not working anymore. Nothing to do with 9/11, just something that was building for years, but took the recession to bring into focus.

There are solutions to this but one thing is for sure: the airlines are going to begin focusing much more on profitability by customer instead of miles flown by customer. This is a major change for the airlines and will make many people unhappy, but it will make other people happy because they can expect to travel on higher fares than cheap leisure fares, but lower fares than today's business fares, with few or no restrictions.