Interesting. When I went to home depot to get a refill on propane, I discovered that they have now automated the whole process. You either insert a credit card or scan in your receipt (wrapped around a credit card amusingly enough). One of those doors will then pop open. Your task is to figure out which. You place the empty container inside and close the door. Another door will pop open and you hunt again. You then take the full container from the spot.

Pretty easy and it beats having to wait around for an associate to show up.