In exchange for a promotional tweet about a discount, American Express rewards its customers by allowing them to get the discount they tweeted about....
Barclaycard Ring cardholders get a voice in setting the terms of their credit cards and a chance to be sharing in the bank's profits from the program....
PayPal takes another stab at the brick-and-mortar checkout with help from Tabbedout, a start-up facilitating mobile payments at restaurants and bars....