Funny, I am working a block from B&H (at 8th between 33 and 34). Its quite an operation to see it live.

You go in and go up to the desk where someone will help you. You select the product and it gets sent from upstairs through a series of tracks running around the store to your salesperson. You looks at and accept the product, then he prints up a receipt and sends the product on its way through the rest of the system. Meanwhile, you go to the cashier and pay for the item where they give you a pickup receipt. then you move to the pick up area where your product is bagged and ready for it.

I guess its fairly efficient, but there are so many people in the store they had to come up with some system.