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Southwest just sent out emails offering double points on all flights between now and November 18, 2015. Unfortunately though, this is only for flights BOOKED AFTER REGISTRATION. So if you already booked a flight and the price has gone down you can cancel and re-book. Remember, Southwest has zero cancelation fees.
The terms do state that only those who received the email qualify, but you might as well registering regardless and see what happens. You can register here.