For the month of November US Airways offered a 100% bonus on purchased miles. They offer a similar promotion typically for at least half the year, and as it turns out they’ve decided to extend the current 100% promotion through this Friday, December 7, 2012.
Anyway, through this promotion miles can be purchased for ~1.88 cents each including tax. You can purchase a maximum of 100,000 miles through this promotion (50,000 base miles and then 50,000 bonus miles), and Dividend Miles accounts have to be at least 12 days old to be eligible for this promotion.
This can be a great deal if you have a specific mileage redemption in mind, and can be an even better deal if you’re just topping off a mileage account. Flying from the US to North Asia via Europe remains just 90,000 miles in business class, so if you outright buy those miles through this promotion you’ll pay $1,700, which is really good. See this post for basics on redeeming Dividend Miles.
My prediction for early 2013? A big devaluation of US Airways’ award chart.