From the Associated Press:

On Friday, Apple Inc. began using the technology at its 254 U.S. stores to send you messages about products, events and other information — tailored to where you are inside, provided you have downloaded the Apple Store app and have given Apple permission to track you.

Using the iBeacon feature, the app will notify you if the computer you ordered is ready for pickup, for example. Show a clerk your screen with the order number, and the clerk will get it for you. Walking by an iPhone table? You may get a message asking if you want to upgrade, check your upgrade availability and see if you can get money for trading in your old phone.

If you’re wondering what all the fuss is about, TidBITS published a great piece on iBeacons back in September.