American is offering up to a 30% bonus on the purchase of AAdvantage miles through December 31, 2013. The bonuses are tiered and based on the number of miles purchased, as follows:
So if you max out the promotion you’re looking at purchasing a total of 78,000 AAdvantage miles (comprised of 60,000 miles — the annual cap on mileage purchases per account — plus an 18,000 mile bonus) for $1,808.75. That’s ~2.32 cents per mile.
Certainly not a rate at which I’d speculatively purchase miles, but at the same time if you have a specific use in mind this could make sense.
Mileage purchases usually take 1-2 days to post, though American allows five day award holds, which means it’s possible to hold something “risk free” while the miles post. Also keep in mind these purchases are processed by points.com, so wouldn’t count as airfare spend for the purposes of your credit card.
(Tip of the hat to Apurva)