“Thanks Again” is a program that offers miles for shopping with small merchants that don’t have their own rewards programs, so far mostly dry cleaners. You register a credit card and when you spend with participating companies you get miles for the transaction, a la iDine (aka Rewards Network).
There aren’t a whole lot of companies working with them, at least so far, so it’s not that attractive. Plenty of folks may be skeptical of giving them credit card numbres, although they do appear quite legitimate. Personally I used a Visa gift card with about $7 left on it, although some might prefer to use one-time use credit card numbers. Why? Signup bonuses.
The program is also available with USAirways (I think) and American but the signup bonuses aren’t as attractive.