I recently bought an iPhone car charger/dock from the Apple Store and was reminded at how good they are at getting the customer in and out of the door quickly and satisfied.
Firstly, I had done my research up front, so I didn't need to ask any questions. All I had to do was spy an open sales clerk and get their attention.
I handed over my credit card. They inserted it into their handheld sales device and asked if I wanted a receipt emailed to the address that they already had on file. They put a nice little thank you sticker on the box so that people didn't think I was a thief and out I strolled. It took all of three minutes.
I know there must be other retailers using this approach, but so far Apple is the only company that I've come across that does it so seamlessly. As much as I love the design of their stores, I also love that I never seem to spend any more time than I have to in them.