Correct me if I am wrong, but up until the end of 2005, Southwest flew to ONE of United's five major hubs (Not SFO, DEN, ORD, or IAD). So there was hardly any route overlap. Now Southwest is moving into DEN. Oh well. That's 2 out of 5. How can you say bye bye United when over 50% of United's revenue comes from international flights, and Southwest does not fly international. Furthermore, Southwest does not fly a single flight to their most profitable hub (SFO), nor do they fly a single flight to their largest hub (ORD).

This seems to be more of a problem for Frontier because they are based solely in Denver. United is spread out all over the globe, and the affect of Southwest should be minimal. Besides, their fuel hedges are running out soon. And what happens when an airline's largest expense doubles???
One thing for sure, Southwest will be forced to raise fares, and the Southwest affect will continue to deteriorate, allowing the industry to rise out of the termoil caused by high oil prices and low cost competition.