Wow, good find! That wasn't obvious in any of the docs that I got with the AAdvantage Business card. 1% savings at the gas station I use regularly, plus 5% on USPS...excellent!
Somehow, this is not mentioned anywhere on FT, so I figured I would bring it up in the main forum.
Aside from the benefit of earning AAdvantage miles on all your purchases, you can earn
cash back on purchases from select companies by registering your CitiBusiness AAdvantage MasterCard with the MasterCard Easy Savings programme. It works like OPEN from American Express, so you don't have to chase down any rebates. All rebates automatically post to your account.
For more details, visit:
http://www.mastercardeasysavings.com/citibusiness?en_US
Ironically, it will not save you anything off your American Airlines purchases, but
you can save 2% on all your CO/UA purchases that are made with a registered card on Continental.com. Neat, eh?
Enjoy!