This morning in Starbucks while discussing the Starbucks card phenomenon, it was mentioned that they could just use RFID to identify your clothing, ask retail partners who purchased it, and if most of the clothes were bought by credit cards that belong to the same person, assume that's you.
Of course, this is a frightening scenario to many, which will drive adverse consumer reaction to such technologies. Unfortunately, negative public opinion does not stop privacy-invasive tech from being deployed, it only means deployment has to be stealthy. So, if Starbucks ends up identifying you as you walk through the door, they will have to keep it quiet and not let you know. This way, we get the privacy invasion without any of the benefits of targeted marketing.
Sure, they could start making your favorite drink before you even get in line, but to do that they'd have to acknowledge they scanned you so they'll just note your presence in a database somewhere, quietly.