When Discounts Go Social on Twitter

Let’s say that you tweet #AMEXcoffee and get a Starbucks discount coupon. Then, you go to Starbucks and purchase a coffee. The offer will be applied as statement credits on your card. No need for discount codes, printouts, or anything else. It’s that simple.
Check out this detailed video explaining the process in full. Is this something you would want your business to participate in? Or is this an invasion of privacy to be avoided?