Remember that this sale is also valid when redeeming Rapid Rewards points. $49 fares are only 2,280 RR points. $99 fares are only 5,280 RR points. etc. You can transfer Chase Ultimate Rewards into Southwest Rapid Rewards instantly at a 1:1 ratio. On top of that, you can now redeem RR points via southwest.com for Airtran flights, which opens up many more routing options.
As an example, I can fly Southwest CLE-BNA or MDW for only 4,560 RR points, or Airtran CAK-MCO or BOS or DEN for only 10,560 RR points ROUNDTRIP. Booking via southwest.com gets you free checked bags. Only downside is Airtran flights booked via southwest.com cannot obtain seat assignments until check-in (24 hours before departure)...and further, seats can only be changed by an agent at the airport.
Flights booked via RR points can be cancelled until 10 minutes prior to departure, and points will be credited back to your RR account with no penalties. This is great for booking tickets for other people.