Between November 1, 2012 and January 31, 2013, US Airways is offering 6,000 bonus miles for three shuttle flights and an additional 12,000 bonus miles for another three shuttle flights (for a total of 18,000 bonus miles after six shuttle flights). Registration is required, and bonus miles post 1-2 weeks after completion of travel. US Airways operates shuttle flights between BOS, DCA, and LGA, so you can earn the bonus on any of those routes. Best of all you don’t actually have to be traveling exclusively between shuttle cities in order to qualify. In other words, flying from TPA to BOS via DCA roundtrip would earn you two “credits,” even though you’re originating in another city.
This is a really lucrative promotion, given that in many cases you can just route via a shuttle city in order to qualify.
(Tip of the hat to New Girl in the Air)