Other airlines have matched Southwest's 50% off sale to/from Vegas, plus added some of their own. Example: Philly to Orlando $64 round-trip. No, we didn't leave off a "1" in front of the "64".
Obviously, lower fuel prices have given airlines some wiggle room to lower fares. But more significantly, people just aren't traveling. Each time the economy sheds another 1/2 million jobs, that's 1/2 million people who probably will not be taking a vacation or going to a business meeting. We see it in our own fare alerts: we'll send out an amazingly low fare that two or three years ago would have gotten clicked on by 75% of those receiving it. That doesn't happen anymore. Let's face it, 2009 will be a rough year. Will the airlines make the mistake they've made in past slumps and cut fares to ridiculous levels? Or will they further cut capacity?
Truth is, there are fewer airlines now--no America West, Aloha, Northwest, Express Jet, Independence Air, etc. to undercut the other carriers. And it seems likely that one or two airlines will cease flying, file Chapter 11, or consolidate, in 2009. That will help the airlines maintain pricing discipline.