As I fly fairly frequently, I usually book my flights as one way flights on Southwest as soon as the dates become available. I check the price frequently. When the price goes down I click the View/Change flights button on their website and choose the lower priced flight. They then issue a credit for travel that needs to be used 1 year from the original purchase date. For example, if you purchase a ticket on August 1, 2009 and the price decreases on October 1st, you can change the reservation. However, the credits need to be used by August 1, 2010. I changed my October flights three times and now have a sizable credit that we can use for our May 2010 trip. You can also cancel a flight if you need to change days/airports and the credit works the same way. I ended up with a 20% off promo code so cancelled my flight and rebooked. Hope this answers your question.
