This trial Wi-Fi application in a German grocery store would make me nuts : When regular shoppers walk in the store they pick up a Tablet PC, swipe their affinity card across a bar code reader on the PC and hang it off their cart. When they swipe their card, the PC receives info via Wi-Fi on what the person has bought historically. Then as they walk into an aisle the PC gets info about things the shoppers have bought before in that aisle so the PC can "remind" shoppers of things they might be forgetting to buy. And it displays advertising about items in the aisle.
The one cool thing about the application is that shoppers scan products on the PC as they put them in their cart. It's not totally clear how this works but it sounds like the PC sends the total cost of the goods via Wi-Fi to a special check out line so that when the shopper checks out their tally is already there and all they have to do is swipe their card to pay.