Here are the details: you must book by May 3rd, and then you can travel May 11 through October 31, 2012. The catch (and isn’t there always one?) is that these discounted airfares are valid for travel on Tuesdays and Wednesdays only. Also, if these fares seem higher than past sale fares, it is because the fares now reflect the mandatory government taxes and fess.
These fares are good in most of the cities where Southwest flies, from Albuquerque to West Palm Beach. The only city not included in this sale is Washington/Dulles.