Netflix U.S. Patent No. 6,584,450. is definitely a fascinating read for a technology aficionado:

4. "MAX OUT"

According to one embodiment, a "Max Out" approach is used to manage the number of items that may be simultaneously rented to customers. According to the "Max Out" approach, up to a specified number of items may be rented simultaneously to a customer. Thus, the "Max Out" approach establishes the size of an inventory of items that may be maintained by customers. The specified number of items may be specific to each customer or may be common to one or more customers. In the present example, if the specified number of items is three, then up to three items may be rented simultaneously by provider 104 to customer 102. If the specified number of items are currently rented to customer 102 and the specified item delivery criteria triggers the delivery of one or more additional items, then those items are not delivered until one or more items are returned by customer 102 to provider 104.

According to one embodiment, in situations where the specified number of items are currently rented to customer 102 and the specified item delivery criteria triggers the delivery of one or more additional items, then the one or more additional items are delivered to customer 102 and customer 102 and a surcharge is applied customer 102. The specified number of items may then be increased thereafter to reflect the additional items delivered to customer 102 and increase the size of the inventory maintained by customer 102. Alternatively, the specified number of items may remain the same and number of items maintained by customer 102 returned to the prior level after items are returned to provider 104 by customer 102. When used in conjunction with the "Max Turns" approach described hereinafter, the specified number of items may be unlimited.

Keep reading the rest of Method and apparatus for renting items at US Patent and Trademark Office.