I didn’t get an email, but apparently I was targeted. They say it’s because I booked a flight with them in 2012. If you did as well, perhaps you were targeted as well.
When you go to the ‘buy miles’ link you are asked to enter your name and account number.
Then if you are targeted you will see the details on the bonus. (If you haven’t been targeted, the offer just appears ‘as usual’ at 3.5 cents per mile plus tax and transaction fee.)
As usual, accounts must be 12 days old or older in order to buy miles and the maximum number of miles eligible for the bonus is 50,000 (meaning you can buy 50,000 miles and receive 50,000 bonus miles – for a total of 100,000).
Oddly, the offer is listed as being valid between September 1 and September 31. It’s a good thing they say they can change the terms without notice, I expect they will change the expiration date of the offer.
US Airways does seem to offer 100% purchase bonuses more often than they have not. Unfortunately, over the past few years they have increased the price of miles, it used to be that you could get a business class ticket to Europe for about $1300 this way and now it’s $1800.
All in all the miles are probably worth the price with the 100% bonus, though I’m not sure I’d stock up speculatively, it really depends on the plans I had for the miles (although if I wanted a specific award, I would top off my account towards that award for sure).