I believe AmEx was the true winner of SXSW for the reasons AdAge states:

It debuted an innovative product. AmEx Sync now allows merchants to offer special offers that consumers can redeem by tweeting an offer to Twitter. There have been enough attempts at Twitter commerce before to warrant some using the shorthand t-commerce, but no company – Twitter included – has done so with such a broad reach, an aggressive marketing campaign, and major brand partners like McDonald's, Whole Foods, and Gulf Oil.