Kudos to my wife for pointing this out, but in recent shopping trips at Target, Safeway and QFC she noticed that how card readers were used impacted the amount of eye contact between the cashier and the shopper. Specifically:
In Target, the card reader takes the card into a machine, and gives the purchaser instructions on what to do. The cashier, without anything to do, bags the items being purchased. The only eye contact that may occur is when the cashier turns the receipt to the purchaser (provided it's not placed directly in the bag)
In Safeway, the overall experience is similar. While the card reader machine does not take the card during the transaction, all instructions are posted on the little card reader screen. Interaction with the cashier is minimal, though they make it a point to thank you by name (provided you have one of their club cards). Presumably this is meant to personalize the experience, however if you have a difficult to prounounce name, it becomes more of a hindrance to that personal touch.
In QFC, the checkout experience is most varied. On the one hand, they have the self-check out stands where you do not need to interact with another human being. On the other hand, the check out experience in a line by a credit card is the most personable of the three stores sampled. Instead of sliding the card and following all instructions on a screen, to run the credit card, you give the card to the cashier. The cashier then hands you a slip to sign, and you return it to them. Though it seems to vary on the cashier, whether or not they check your signature, the amount of eye contact, and potential eye contact puts both Target and Safeway to shame.
There are no profound insights here regarding credit card readers, or customer loyalty programs. Rather, the only observation here is on how tech can help or hinder actual interaction between people depending on how it is used.