The American Express-Twitter coupons marriage is going so well that some of the merchant partners have already had to increase their cap limit to accommodate demand. Twitter’s viral nature seems to be driving a tidal wave of coupons getting nabbed by consumers. Within the first 48 hours, Amex saw more than 2,000 tweets with the #AmexMcDonalds hash tag, with customers sharing what they planned to order. By tweeting hashtag #AmexWholefoods, consumers receive $20 off purchases of $75 or more at the natural foods market made with their Amex cards. McDonald’s is offering a $5 discount through its #AmexMcDonalds hashtag. Best Buy, FTD, Zappos.com, Century 21 department stores, Gulf Oil, Cheese Factory, FexEx Office, Sports Authority, Seamless.com, and Ticketmaster are other launch partners in the effort. The @AmexSync account tweets confirmation of enrollment to receive the deal. Then, when consumers make qualified purchases, they receive the appropriate credit on their synced cards within days.