That's a source of disagreement with Democrats, who want to see lower-income folks who pay Social Security but not income taxes get relief in the form of a rebatecheck too.
With Amex-Foursquare, you link your credit card to your Foursquare account and then check in using Foursquare at a designated merchant and get a discount or rebate applied to your card.
Taxpayers who did not receive a check in the mail but were otherwise entitled to a check could have the stimulus applied towards their taxes due in the form of the Rebate Recovery Credit.