This has lead to a frequent flyer miles scam in which people buy thousands of dollars worth of these coins on their credit card, only to take them to the bank days later and pay off the card immediately. As news of this scam reached the public eye, the US mint put restrictions on purchasing these coins to $1000 worth every 10 days. Still, 3,000 free miles each month isn't a bad way to rack up cheap travel.

It is the general public that really get harmed by scams like this in that frequent flyer programs will get stricter and their tax dollars get to pay the tab on all the transactions involved in both the shipping and exchanging of the currency. My suggestion: stick to paper money. Many people have switched to credit or debit, but people are not going to go back to carrying a satchel of gold coins.
Yahoo Finance: Fly-for-free